Subtraction 1.3. Overcoming Math Anxiety

Transcription

1 1.3 Subtraction 1.3 OBJECTIVES 1. Use the language of subtraction 2. Subtract whole numbers without borrowing 3. Solve applications of simple subtraction 4. Use borrowing in subtracting whole numbers 5. Solve applications that require borrowing Overcoming Math Anxiety Hint #3 Don t procrastinate! 1. Do your math homework while you re still fresh. If you wait until too late at night, your tired mind will have all that much more difficulty understanding the concepts. 2. Do your homework the day it is assigned. The more recent the explanation is, the easier it is to recall. 3. When you ve finished your homework, try reading the next section through once. This will give you a sense of direction when you next hear the material. This works whether you are in a lecture or lab setting. Remember that, in a typical math class, you are expected to do two or three hours of homework for each weekly class hour. This means two or three hours per night. Schedule the time and stay to your schedule. NOTE By opposite we mean that subtracting a number undoes an addition of that same number. Start with 1. Add 5 and then subtract 5. Where are you? We are now ready to consider a second operation of arithmetic subtraction. In Section 1.2, we described addition as the process of combining two or more groups of the same kind of objects. Subtraction can be thought of as the opposite operation to addition. Every arithmetic operation has its own notation. The symbol for subtraction,, is called a minus sign. When we write 8 5, we wish to subtract 5 from 8. We call 5 the subtrahend. This is the number being subtracted. And 8 is the minuend. This is the number we are subtracting from. The difference is the result of the subtraction. To find the difference of two numbers, we will assume that we wish to subtract the smaller number from the larger. Then we look for a number which, when added to the smaller number, will give us the larger number. For example, because This special relationship between addition and subtraction provides a method of checking subtraction. Rules and Properties: Relationship Between Addition and Subtraction The sum of the difference and the subtrahend must be equal to the minuend. 29

2 30 CHAPTER 1 OPERATIONS ON WHOLE NUMBERS Example 1 Subtracting a Single-Digit Number Check: Our check works because 12 5 asks for the number that must be added to 5 to get 12. Difference Subtrahend Minuend CHECK YOURSELF 1 Subtract, and check your work The procedure for subtracting larger whole numbers is similar to the procedure for addition. We subtract digits of the same place value. Example 2 Subtracting a Larger Number Step 1 Step 2 Step To check: Add We subtract in the ones column, then in the tens column, and finally in the hundreds column. The sum of the difference and the subtrahend must be the minuend. CHECK YOURSELF 2 Subtract, and check your work You know that the word difference indicates subtraction. There are other words that also tell you to use the subtraction operation. For instance, 5 less than 12 is written as 12 5or7 20 decreased by 8 is written as 20 8or12

3 SUBTRACTION SECTION Example 3 Translating Words That Indicate Subtraction Find each of the following. (a) 4 less than 11 4 less than 11 is written (b) 27 decreased by 6 27 decreased by 6 is written CHECK YOURSELF 3 Find each of the following. (a) 6 less than 19 (b) 18 decreased by 3 Units Analysis This is the first in a series of essays that are designed to help you solve applications of mathematics. Questions in the exercise sets will require the skills that you build by reading these essays. A number with a unit attached (like 7 feet or 26 mpg) is called a denominate number. Any genuine application of mathematics will involve denominate numbers. When adding or subtracting denominate numbers, the units must be identical for both numbers. The sum or difference will have those same units. Examples: $4 $9 $13 (notice that, although we write the dollar sign first, we read it after the quantity, as in four dollars ) 7 feet 9 feet 16 feet 39 degrees 12 degrees 27 degrees 7 feet 12 degrees yields no meaningful answer! 3 feet 9 inches yields a meaningful result only if the 3 feet is converted into 36 inches. We will discuss conversion of units in later essays. Now we consider subtraction word problems. The strategy is the same one presented in Section 1.2 for addition word problems. It is summarized with the following four basic steps. Step by Step: Step 1 Step 2 Step 3 Step 4 Solving Subtraction Applications Read the problem carefully to determine the given information and what you are asked to find. Decide upon the operation (in this case, subtraction) to be used. Write down the complete statement necessary to solve the problem and do the calculations. Check to make sure you have answered the question of the problem and that your answer seems reasonable.

4 32 CHAPTER 1 OPERATIONS ON WHOLE NUMBERS Let s work an example using these steps. Example 4 Setting Up a Subtraction Word Problem Tory has $37 in his wallet. He is thinking about buying a $24 pair of pants and a $10 shirt. If he buys them both, how much money will he have? First we must add the cost of the pants and the shirt. $24 $10 $34 Now, that amount must be subtracted from the $37. $37 $34 $3 He will have $3 left. CHECK YOURSELF 4 Sonya has $97 left in her checking account. If she writes checks for $12, $32, and $21, how much will she have in the account? Difficulties can arise in subtraction if one or more of the digits of the subtrahend are larger than the corresponding digits in the minuend. We will solve this problem by using a process called borrowing. First, we ll look at an example in expanded form. Example 5 Subtracting When Borrowing Is Needed Do you see that we cannot subtract in the ones column? Regrouping, we borrow 1 ten in the minuend and write that ten as 10 ones: 50 2 becomes or We now have We can now subtract as before or 25 In practice, we will use a more convenient short form for the subtraction We indicate the fact that we have borrowed 1 ten by putting a slash through the 5 and then writing 4 tens. Add 10 ones to the original 2 ones to get 12 ones. We 27 can then subtract. 25 Check:

5 SUBTRACTION SECTION CHECK YOURSELF 5 Subtract, and check your work Let s work through another subtraction example that will require a number of borrowing steps. Here, zero appears as a digit in the minuend. Example 6 Subtracting When Borrowing Is Needed 4 1 Step In this first step we borrow 1 ten. This is written as 10 ones and combined with the original 3 ones. We can then subtract in the ones column. NOTE Here we borrow 1 thousand; this is written as 10 hundreds. Step We must borrow again to subtract in the tens column. There are no hundreds, and so we move to the thousands column. NOTE We now borrow 1 hundred; this is written as 10 tens and combined with the remaining 4 tens. Step The minuend is now renamed as 3 thousands, 9 hundreds, 14 tens, and 13 ones. Step The subtraction can now be completed. To check our subtraction: CHECK YOURSELF 6 Subtract, and check your work You will need to use both addition and subtraction to solve some problems, as Example 7 illustrates. Example 7 Solving a Subtraction Application Bernard wants to buy a new piece of stereo equipment. He has $142 and can trade in his old amplifier for $135. How much more does he need if the new equipment costs $449?

6 34 CHAPTER 1 OPERATIONS ON WHOLE NUMBERS First we must add to find out how much money Bernard has available. Then we subtract to find out how much more money he needs. $142 $135 $277 The money available to Bernard $449 $277 $172 The money Bernard still needs CHECK YOURSELF 7 Martina spent $239 in airfare, $174 for lodging, and $108 for food on a business trip. Her company allowed her $375 for the expenses. How much of these expenses will she have to pay herself? CHECK YOURSELF ANSWERS (a) 13; (b) $32 Check: To check: Check: $239 $ $146 $521 Total expenses Total expenses Amount allowed

7 Name 1.3 Exercises Section Date 1. In the statement is called the 6 is called the 3 is called the Write the related addition statement. 2. In the statement is called the 2 is called the 7 is called the Write the related addition statement. In exercises 3 to 26, do the indicated subtraction, and check your results by addition , , ,047 25, , , ,000 17,900 28,700 23,458 ANSWERS , , Find the number that 28. Find the number that 29. Find the number that is 25 less than 76. results when 58 is is the difference decreased by 23. between 97 and Find the number that 31. Find the number that 32. Find the number that is is 125 less than 265. results when 298 is the difference between decreased by and

8 ANSWERS Based on units, determine if the following operations produce a meaningful result miles 4 miles 34. $560 $ feet 11 inches F 6 C yards 10 yards mi/hr 6 ft/sec In exercises 39 to 42, for various treks by a hiker in a mountainous region, the starting elevations and various changes are given. Determine the final elevation of the hiker in each case. 39. Starting elevation 1053 feet, increase of 123 feet, decrease of 98 feet, increase of 63 feet. 40. Starting elevation 1231 feet, increase of 213 feet, decrease of 112 feet, increase of 78 feet. 41. Starting elevation 7302 feet, decrease of 623 feet, decrease of 123 feet, increase of 307 feet. 42. Starting elevation 6907 feet, decrease of 511 feet, decrease of 203 feet, increase of 419 feet. Solve the following applications. 43. Test scores. Shaka s score on a math test was 87 and Tony s score was 23 points less than Shaka s. What was Tony s score on the test? 44. New pay. Duardo s monthly pay of $879 was decreased by $175 for withholding. What amount of pay did he receive? 45. Number problem. The difference between two numbers is 134. If the larger number is 655, what is the smaller number? 46. Family budget. In Jason s monthly budget, he set aside $375 for housing, and $165 less than that for food. How much did he budget for food? 47. Consumer purchases. Inez has $228 in cash and wants to buy a television set that costs $449. How much more money does she need? 36

9 ANSWERS 48. Construction. The Sears Tower in Chicago is 1454 feet (ft) tall. The Empire State Building is 1250 ft tall. How much taller is the Sears Tower than the Empire State Building? Education. A college s enrollment was 2479 students in the fall of 1999 and 2653 students in the fall of What was the increase in enrollment? 50. Net pay. In one week, Margaret earned $278 in regular pay and $53 for overtime work, and $49 was deducted from her paycheck for income taxes and $18 for social security. What was her take-home pay? 51. Savings. Rafael opened a checking account and made deposits of $85 and $272. He wrote checks during the month for $35, $27, $89, and $178. What was his balance at the end of the month? 52. Dieting. Dalila is trying to limit herself to 1500 calories per day (cal/day). Her breakfast was 270 cal, her lunch was 450 cal, and her dinner was 820 cal. By how much was she under or over her diet? 53. Recreation. A professional basketball team scored 98, 136, and 113 points in three games. If its opponents scored 102, 109, and 93 points, by how much did the team outscore its opponents? 54. Checking account balance. To keep track of a checking account, you must subtract the amount of each check from the current balance. Complete the following statement. Beginning balance $351 Check #1 29 Balance Check #2 139 Balance Check #3 75 Ending balance 37

10 ANSWERS Expense accounts. Complete the following record of a monthly expense account. Monthly income $1620 House payment 343 Balance Car payment 183 Balance Food 312 Balance Clothing 89 Amount remaining 56. Education. A course outline states that you must have 540 points on five tests during the term to receive an A for the course. Your scores on the first four tests have been 95, 84, 82, and 89. How many points must you score on the 200-point final to receive an A? 57. Travel. Carmen s frequent-flyer program requires 30,000 miles (mi) for a free flight. During 1999 she accumulated 13,850 mi. In 2000 she took three more flights of 2800, 1475, and 4280 mi. How much further must she fly for her free trip? 58. Budget. Peter, Paul, and Mary all submitted advertising budgets for a student government dance. Ad Medium Peter Paul Mary Radio ads $500 $600 $300 Newspaper ads $150 $200 $150 Posters $225 $250 $275 Hand bills $175 $150 $250 If $900 is available for advertising, how much over budget would each student be? 59. Farming. The value of all crops in the Salinas Valley in 1998 was about $2 billion. The top four crops are listed below. (a) How much greater is the combined value of both types of lettuce than broccoli? (b) How much greater is the value of the lettuce and broccoli combined than the strawberries? Crop Head lettuce Broccoli Leaf lettuce Strawberries Crop value, in millions $210 $198 $246 $360 38

11 ANSWERS Complete the magic squares Efrain has lost track of his checking account transactions. He knows he started with $50 and has deposited $120, $85, and $120. He also knows he has withdrawn $200 and $55. He just can t remember the order in which he did all this. (a) What is Efrain s balance after all these transactions? (b) Does the order of the transactions make any difference from the math point of view? (c) Does the order of transactions make any difference from the banking point of view? Explain your answers. 65. Using the World Wide Web, determine the population of Arizona, California, Oregon, and Pennsylvania in each of the last three censuses. (a) Find the total change in each state s population over this period. (b) Which state shows the most change over the past three censuses? (c) Write a brief essay describing the changes and any trends you see in this data. List any implications that they might have for future planning. 66. Describe in words each of the following equations. (Make sure you use a complete sentence.) Then exchange your sentence with other students and see if their interpretations result in the same equation you used. (a) (b) Evaluate the following two expressions: (1) 8 (4 2) (2) (8 4) 2 Do you obtain the same answer? What conclusion can you draw about subtraction and an associative property? 39

12 ANSWERS Think of any whole number. Add 5. Subtract 3. Subtract two less than the original number. What number do you end up with? Check with other people. Does everyone have the same answer? Can you explain the results? Answers 1. 9 is the minuend, 6 is the subtrahend, and 3 is the difference , , , Yes 35. No 37. Yes ft ft $ students 51. $ points 55. See exercise mi 59. (a) $324,000,000; (b) $618,000,

13 Using a Scientific Calculator to Subtract NOTE Particularly after working with borrowing in subtraction, you may be tempted to use your calculator for problems besides the ones in these special calculator sections. NOTE Remember, the point is to brush up on your arithmetic skills by hand, along with learning to use the calculator in a variety of situations. Now that you have reviewed the process of subtracting by hand, let s look at the use of the calculator in performing that operation. To compute 56 29, follow the indicated calculator steps. 1. Press the clear key. 2. Enter the first number Press the minus key. 4. Enter the second number Press the equals key. The display shows 27 C The difference, 27, will now be in the display. The calculator can be very helpful in a problem that involves both addition and subtraction operations. Example 1 Using a Scientific Calculator to Subtract NOTE As with addition, the same steps are used on a graphing calculator, except we press ENTER rather than. Find Enter the numbers and the operation signs exactly as they appear in the expression Display 37 An alternative approach would be to add 23 and 56 first and then subtract 13 and 29. The result is the same in either case. CHECK YOURSELF 1 Find CHECK YOURSELF ANSWERS

14 Name Section ANSWERS Date Calculator Exercises Do the indicated operations , ,243 49, ,500 78, Subtract 235 from the sum of 534 and Subtract 476 from the sum of 306 and Solve the following applications. 9. Gas sales. Readings from the Fast Service Station s storage tanks were taken at the beginning and the end of a month. How much of each type of gas was sold? What was the total sold? 11. Super Regular Unleaded Unleaded Total Beginning reading 73,255 82,349 81,258 End reading 28,387 19, Gallons used The land areas, in square miles (mi 2 ), of three Pacific coast states are California, 158,693 mi 2 ; Oregon, 96,981 mi 2 ; Washington, 68,192 mi How much larger is California than Oregon? 11. How much larger is California than Washington? Answers , Regular, 44,868 gal; unleaded, 62,696 gal; super unleaded, 72,604 gal; total, 180,168 gal ,501 mi 2 42