Ray's New Practical Arithmetic · Art. 154 · Unit 12: Decimal Fractions (continued)
72. Decimals: promiscuous (mixed) examples
Goal: Your child chooses the right decimal operation for mixed money and measure problems.
You'll need
- Paper and pencil, or a slate or small whiteboard
What's in the book
Pages 187–188 hold "Promiscuous Examples" (Art. 154): about 19 mixed word problems on costs, quantities and measures, each with its printed answer.
The lesson, step by step
Warm-up
Explain the old word: "promiscuous examples" just means mixed problems, in no special order. Your child has to decide which operation each one needs.
Ask the three questions
For each problem, have your child say aloud: What do I know? What do I want? Do I multiply or divide?
Cost of many = price of one × number. Number you can buy = money ÷ price of one.
Work an example together
What is the cost of 9 yd. flannel, at $0.40 per yard, and 12 yd., at $0.75 per yard?
9 × .40 = $3.60; 12 × .75 = $9.00; total $12.60.
Guided practice
Do these two together:
What is the cost of 16.25 yd. of cloth, at $2.6875 per yard?
At $0.75 per bushel, how much wheat can be bought for $35.25?
The first multiplies; the second divides.
Independent practice and check
Your child works problems 2 and 5–19. The ones with mixed units (like "14 bu. 3 pk. 4 qt.") need the measure into a decimal first, from the last guide. 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: 4 yd. at $0.25; 10 lb. at $0.15; how many 5-cent pencils for $1?
Tip
Some answers have many decimal places (like $43.671875) because Ray uses exact figures. Accept the exact answer, then ask your child to round it to the nearest cent.