Lesson 1 3 Core Focus on Decimals Fractions

Lesson 1. 3 Core Focus on Decimals & Fractions Measuring in Centimeters

Warm-Up 1. Which is larger, 5. 4 or 5. 7? 5. 7 2. Which is smaller, 4. 8 or 4. 3? 4. 3 3. Write the decimal that represents the following words: eight and five tenths. 8. 5 4. Write the decimal that represents the following words: eleven and four tenths. 11. 4

Lesson 1. 3 Measuring in Centimeters Measure and draw line segments using centimeters.

Vocabulary Metric System A decimal system of measurement. The metric system is used in a majority of countries around the world. The basic unit of length in the metric system is the meter. Other metric units, such as millimeters, centimeters, and kilometers, are based on the meter.

Vocabulary Continued… Tick Marks The metric ruler is divided up using tick marks. Tick marks are equally divided spaces marked with a small line. cm 1 cm 6 and cm = 6. 3 cm Each whole number on a metric ruler represents a centimeter (cm). The small tick marks between each centimeter represent millimeters (mm). There are 10 millimeters in 1 centimeter. One millimeter is onetenth of a centimeter.

Example 1 Find the length of the line to the nearest tenth of a centimeter. Line up the 0 mark on the ruler with the left edge of the line. Identify the tick mark that represents the length of the line. Each small tick mark represents 0. 1 centimeters. Count the number of tick marks after the last whole number to find the number of tenths. 6 + 0. 3 = 6. 3 cm WHOLE NUMBER + TENTHS = TOTAL LENGTH The length of the line is 6. 3 cm.

Explore! Using A Metric Ruler Step 1 Use your ruler to measure the length of each object below to the nearest tenth of a centimeter. Record your answers. Step 2 Sometimes measurements are approximated to the nearest half centimeter. a. Round each of the measurements from Step 1 to the nearest half centimeter. b. What two decimal numbers can the measurements end with if they are rounded to the nearest half centimeter?

Explore! Using A Metric Ruler Step 3 Draw a line that fits each description. a. exactly 3. 6 centimeters long b. exactly 0. 8 centimeters long c. approximately 7 centimeters long d. exactly 7 centimeters long e. approximately 3. 5 centimeters long f. approximately 1. 5 centimeters long Step 4 Are the lines from part c and d in Step 3 the exact same length? Do they have to be? Why or why not? Step 5 Estimate how long your pencil is in centimeters. Record your estimate. Measure your pencil to see how long it is. How far off was your estimate to the nearest tenth of a centimeter? Step 6 Estimate the length (in centimeters) of two other objects in your classroom. measure the objects to the nearest half centimeter. Approximately how far off were your estimates?

Example 2 Find the length of the line to the nearest half centimeter. Line up the 0 mark on the ruler with the left edge of the line. 8. 8 Identify the tick mark that represents the length of the line. The line is approximately 9 centimeters long. 8. 8 is closer to 9. 0 centimeters than 8. 5

Communication Prompt How is measuring with centimeters related to decimals?

Exit Problems 1. Draw and label a line that is 2. 4 cm long. 2. Draw and label a line that is 9. 9 cm long. 3. Draw and label a line that is 7. 5 cm long. 4. Measure ______ to the nearest centimeter (fill in the blank with an item you have with you). Answers Vary