Grade 3 Lesson 18: Building a Ruler, Measuring & Rounding TEACHER MODELING/STUDENT COMMUNICATION

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1 Grade 3 Lesson 18: Building a Ruler, Measuring & Rounding Purpose: Materials: To build a 1-foot ruler and use it for measuring Masters "1-Foot Ruler", Two Transp. 1-foot Rulers (Transparency Kit), Fraction Bars TEACHER MODELING/STUDENT COMMUNICATION Masters 1-Foot Ruler pencils Transp "1-Foot Ruler" Fraction Bars small objects Paper and pencils transp. bars Activity 1 Building a 1-foot ruler 1. Each student will need the Masters "1-Foot Ruler" and a pencil. You have a ruler on your sheet that is one foot long. How many equal parts is it divided into? (12) What is the length of one of these parts? (One inch.) Some students may say 1/12 of a foot, and if so, acknowledge this as correct. Beneath the marks on your ruler, write the numbers 1 through 12 for the 12 inches in a foot. 2. Place your transparent 1-Foot Ruler on the overhead and illustrate your handspan or have a volunteer show their handspan. Measure the length of your handspan by placing your thumb or little finger on the zero mark. How many of you have a handspan under 6 inches? Over 6 inches? How many of you have a handspan that is between two marks on your ruler? (Discuss this problem and ask students for a solution.) How can we find a measurement if a handspan falls between two marks? (Round the measurement off to the nearest inch.) What is the measure of your handspan to the nearest inch? Does anyone have a handspan that is halfway between two marks? What can be done in this case? (Rounding up is one possibility and another is placing halfway marks between each mark on the ruler, which is done next. 3. Distribute a deck of bars to each group. Place any orange bar between 0 and 6 on your ruler so that its edge is on the dashed line above zero, and make halfway marks for each inch. Illustrate this by taping an orange bar to a Masters copy of the ruler and make halfway marks on the ruler - red marks below. Place the edge of an orange bar between 6 and 12 and continue to make halfway marks.

2 Write the fraction 1/2 on your ruler for the mark between 0 and 1, and then write the mixed numbers 1 1 2, 2 1, etc., for the halfway points between the 2 numbers on your line. Measure your handspan again to the nearest mark, now that your ruler has the halfway marks. Ask for examples of measurements. Raise your hand if you still have a measurement between one of the marks on your ruler. Discuss this problem and the two types of solutions from above, that is, rounding and inserting more marks. 4. Place your "Transparent 1-Ruler with Halves" on the overhead and place a colored mark halfway between 0 and 1/2, and then place another mark that is half way between 1/2 and 1. What are the fractions for these two new marks? Explain your reasoning. (1/4 and 3/4 because the line between 0 and 1 is divided into four equal parts. Insert a few more quarter marks, but not the numbers, one at a time, and ask for the mixed numbers for these marks. It is not necessary for the students to place quarter marks on their rulers. Perhaps this can be done after they have done some measuring with the rulers. Activity 2 Measuring objects in the room Pass out scissors and ask students to carefully cut along the dotted lines of their rulers. Pair the students up with a partner for the following activity. Select something from the room such as a book, desk, table, etc. and measure it with your ruler. By working with your partner, you can alternately place your two rulers end to end to measure large objects. Look at some of their examples. In particular, discuss measurements of more than one foot and how they should be recorded. For example, lengths of "1 foot and 4½ inches," or 3 feet 7½ inches Ask students to write their names on the back of their rulers. Collect these rulers for use with the two Activity Sheets for this lesson. INDEPENDENT PRACTICE and ASSESSMENT Activity Sheet #18A Using a one-foot ruler to measure the lengths of objects Activity Sheet #18B Using a one-foot ruler to measure the lengths of physical objects fractionbars.com Set 2 Hitting Asteroids - Benchmark Whole Numbers (rounding mixed numbers to whole numbers and aiming laser beams)

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4 Grade 3 Activity Sheet #18A Name: The length of this crayon is between 3 inches and 3 and ½ inches, but it is closer to 3 and ½ inches. So, its length to the nearest ½ inch is 3 and ½ inches. 3 ½ inches Use the ruler you built or any 1-foot ruler to measure each length to the nearest ½ inch. 1. The longer side of this sheet of paper. inches 2. The shorter side of this sheet of paper. inches 3. The length of this pencil. inches 4. The width and length of this rectangle: width inches; length inches width length 5. Write the six missing lengths for this figure.

5 Grade 3 Activity Sheet #18B Name: A person's arm-span is the distance between the tips of their fingers when their arms are outstretched like mine. With the help of a classmate, and using the ruler you built in class or another ruler, measure your arm-span to the nearest inch. For example, the length of this rectangle is between 5 and 6 inches, but it is closer to 5 inches than 6. So, its length to the nearest inch is 5 inches. 5 inches 1. Your arm-span: feet and inches Find some objects to measure with your ruler or with a yardstick or tape measure. Describe the object and measure its length to the nearest inch. 2. An object between 1 and 2 feet. Length: 1 foot and inches 3. An object between 2 and 3 feet. Length: 2 feet and inches 4. An object between 3 and 4 feet. Length: 3 feet and inches 5. An object longer than 4 feet. Length: feet and inches