Ray's New Practical Arithmetic · Arts. 157–159 · Unit 13: The Metric System
74. Metric land, capacity and weight
Goal: Your child converts among ars, hektars and centars; liters and hektoliters; grams and kilograms.
You'll need
- Paper and pencil, or a slate or small whiteboard
What's in the book
Page 192 gives Land Measure (Art. 157) and Measures of Capacity (Art. 158). Page 193 has remarks, capacity problems and Measures of Weight (Art. 159), and page 194 the weight problems. Answers are printed.
The lesson, step by step
Warm-up
Ask: How many centimeters in a meter? How many meters in a kilometer? The same prefixes work for every metric measure.
Land
The ar (today usually spelled "are") is 100 square meters. The book's table: 100 centars = 1 ar; 100 ars = 1 hektar. Ray notes that the hektar is very nearly 2½ acres.
Since these steps are 100, the point moves two places at a time.
Capacity and weight
Ray gives the legal U.S. values:
The Gram is the unit of Weight; it is legal at 15.432 grains.
The liter was legal at 1.0567 quarts.
The measures commonly used are the liter and hektoliter.
For measuring wood the ster is used; it is a cubic meter.
Guided practice
Do one of each together: reduce 2.625 a. to centars (page 192); reduce 873.5 l. to hektoliters (page 193); reduce .28 Kg. to grams (page 194).
Independent practice and check
Your child works the rest of the land, capacity and weight problems on pages 192–194. 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
Aloud: 1500 g = ? kg; 3 l = ? cl; 1 Ha = ? a; 2.4 Dl = ? l.