Estimating/ Rounding

Estimating/ Rounding

UStandard: 3.A.1.1 UConcept Skill: UEstimating/Rounding To estimate means to find an answer that is close to an exact amount. To round means to find about how many or how much by expressing a number to the nearest ten, hundred, thousand, and so on. On way of estimating is by looking at a picture without counting each object. You can estimate for math problems by comparing one diagram to another. When rounding, find the place value you are rounding to. If you are rounding to the nearest ten, find the tens place. If you are rounding to the nearest hundred, find the hundreds place. Look at the place value to the right. If you are rounding to the nearest ten, look at the ones place. If you are rounding to the nearest hundred, look at the tens place. If that digit is 0, 1, 2, 3, or 4, round down. If that digit is 5, 6, 7, 8, or 9, round up.

For example, to round 73 to the nearest ten: Find the place value you are rounding to. You are rounding to the nearest ten, so find the tens place: U7U3. Look at the place value to the right. You are rounding to the nearest ten, so look at the ones place: 7U3U. That digit is a 3. That means that you should round down to the nearest ten. The nearest ten is 70, so round 73 down to 70. You can round numbers to help you solve problems. For example, adding 49 and 22 is difficult to do in your head. If you round the numbers first, you can find an estimated answer that is close to the exact answer.

Teacher Sample Questions Example: 1 Melanie and Desiree both have containers with pencils. Melanie s Desiree s Does Melanie have less than, more than, or the same number of pencils as Desiree? Step 1: Compare the two containers/diagrams. (The first looks like it is completely full. The second diagram looks almost empty. Step 2: Decide how the pencils compare. (Melanie s container is fuller than Desiree s. Melanie has more pencils than Desiree).

Example: 2 Estimate 138 + 73 Step 1: Round the first number to the nearest ten. (Find the tens place: 1U3U8). Look at the place value to the right, the ones place: 12U8U. Step 2: Decide whether to round up or down. (The digit in the ones place is 8, so I have to round up). 138 rounds up to 140 Step 3: Round the second number to the nearest ten. (Find the tens place: U7U3). Look at the place value to the right, the ones place: 7U3U. Step 4: Decide whether to round up or down. (The digit in the ones place is 3, so I have to round down. 73 rounds down to 70 Step 5: What is your estimated answer? (A good estimate for 138+73 is 140+70=210

STUDENT PRACTICE If the length of the car shown above is about nine feet, the length of the van is about A. eight feet B. twelve feet C. eighteen feet D. twenty feet Felix wants to add 78 and 37. Which of the following would be best for Felix to use to estimate the sum? A. 80 + 30 B. 90 + 20 C. 80 + 40 D. 90 + 40 A ticket to the dolphin show costs $18 for 1 adult. Which is the closest to the total cost of tickets for 4 adults? A. $20 B. $40 C. $80 D. $120

KEY If the length of the car shown above is about nine feet, the length of the van is about A. eight feet *B. twelve feet C. eighteen feet D. twenty feet Felix wants to add 78 and 37. Which of the following would be best for Felix to use to estimate the sum? A. 80 + 30 B. 90 + 20 *C. 80 + 40 D. 90 + 40 A ticket to the dolphin show cost $18 for 1 adult. Which is the closest to the total cost of tickets for 4 adults? A. $20 B. $40 *C. $80 D. $120

STUDENT PRACTICE If the stack of books shown above is 2 feet high, then about how tall is the light pole? A. 3 feet B. 6 feet C. 12 feet D. 20 feet The school auditorium has 99 seats. People are sitting in 68 of the seats. Which is the best estimate of the number of seats that do not have people sitting in them? Use words, numbers, or pictures to show your answer.

KEY If the stack of books shown above is 2 feet high, then about how tall is the light pole? A. 3 feet B. 6 feet *C. 12 feet D. 20 feet The school auditorium has 99 seats. People are sitting in 68 of the seats. Which is the best estimate of the number of seats that do not have people sitting in them? Use words, numbers, or pictures to show your answer. 99 rounds to 100 68 rounds to 70 100 70 = 30