Ray's New Practical Arithmetic · Arts. 160–161 · Unit 13: The Metric System
75. Metric and old measures compared
Goal: Your child uses a table of values to change metric measures to the old American ones and back, and works mixed metric problems.
You'll need
- Paper and pencil, or a slate or small whiteboard
What's in the book
Page 194 gives a table of legal and approximate values (meter = 39.37 in., kilometer = .62137 mile, kilogram = 2.2046 lb., and more) with a worked example. Page 195 has problems 2–10 and Miscellaneous Examples (Art. 161), which continue on page 196.
The lesson, step by step
Warm-up
Ask your child to guess: Is a kilometer longer or shorter than a mile? (Shorter, about 5/8 mile.) Is a kilogram more or less than a pound? (More, about 2.2 pounds.)
The idea
Read the line under the table:
The legal value is used in solving the following examples.
So to change meters to inches, multiply by 39.37. To change pounds to kilograms, divide by 2.2046.
Work the book's example
How many yards, feet, etc., in 4 m.?
4 × 39.37 = 157.48 in. Divide by 12: 13 ft. 1.48 in. Divide the feet by 3: 4 yd. 1 ft. So the answer is 4 yd. 1 ft. 1.48 in.
Guided practice
Do these two together:
What is the value of 36 lb. in kilograms?
How many hektars in 160 acres?
(160 acres was a common farm size in 1877.)
Independent practice and check
Your child works problems 3–10 on page 195 and Miscellaneous Examples 1–12 on pages 195–196. The book prints the answer at the end of each problem line. Have your child cover the answers with a strip of paper, work the problem, then slide the strip down to check.
Mental-math wrap-up
Using the approximate values: 8 km is about how many miles? 10 kg is about how many pounds? 2 m is about how many feet?
Tip
Old measures note: some old units here (rods, pennyweights, cords) are explained in the earlier tables of the book. A rod is 16½ ft.; a cord of wood is 128 cubic feet.