Ray's New Intellectual Arithmetic · Lesson XII · Unit 2: Multiplying and dividing
12. Multiplying: the cost of several
Goal: Your child finds the cost of several things from the cost of one, and explains with “times”.
You'll need
- The book page (press “📖 Book page”, or use a printed copy)
- Paper for jotting, though the work is meant to be done in the head
What's in the book
Twenty-two cost and “times” problems, answered like “Ans. 4 cents. Why? Because 2 times 2 are 4.”
The lesson, step by step
Warm up
Ask three or four problems from the last lesson again, out of order. Your child answers and says why.
Show the reasoning
SayAt 3 cents apiece, 4 apples cost 4 times 3 cents, which are 12 cents.
Multiplying is a quick way of adding the same number again and again.
Work the problems aloud
Read each problem on the page aloud. Your child answers, then explains in a full sentence, the way the book's model solutions do. The problems go like this:
At 3 cents apiece, what will 4 apples cost?
At 6 dollars a barrel, what will 4 barrels of flour cost?
If 1 marble is worth 7 apples, how many apples are 5 marbles worth?
Ask “Why?”
After each answer ask “Why?” or “How do you know?” Ray's wants the reasoning said aloud, not just the number. If your child stalls, go back to the model and say the first half of the explanation together.
Wrap up
Pick the two problems that were hardest today. Tomorrow, start with those as the warm-up.
Afterwards
Do the rest of the lesson's problems over the next day or two, a few at a time. Move on when your child can explain them without help.
Answers to the book's problems
1) 4 cents. 2) 6. 3) 8. 4) 9. 5) 12. 6) 15. 7) 16. 8) $20. 9) $24. 10) 25. 11) 30. 12) 36. 13) 14. 14) 21. 15) 28. 16) 35 apples. 17) 16 apples. 18) 24, 32 cents. 19) 40 apples. 20) 18, 27 cents. 21) 40 cents. 22) 33 cents.
Worked out for this site from the scan. If a number in your copy differs, trust the book. Every answer is in Ray's own Key ↗.