Ray's New Practical Arithmetic · Art. 79 · Unit 8: Operations with Compound Numbers
44. Multiplying compound numbers
Goal: Your child multiplies a measure with several units, starting from the smallest unit and carrying by the table.
You'll need
- The book
- A slate, small whiteboard or scrap paper
- A notebook and pencil
What's in the book
Multiplication of compound numbers: definition, a worked example, rule, proof and remarks, then problems 2 to 15 with printed answers.
The lesson, step by step
Warm-up
Mental: 3 × 2 pk.? (6 pk. = 1 bu. 2 pk.) 4 × 20 min.? (1 hr. 20 min.)
The idea
Read:
When the multiplicand is a compound number, the operation is called Multiplication of Compound Numbers.
Work the book's example: 5 bags of wheat, each 2 bu. 3 pk. 5 × 3 pk. = 15 pk. = 3 bu. 3 pk.; write 3 pk. and carry 3 bu. 5 × 2 bu. = 10, + 3 = 13 bu. Total 13 bu. 3 pk.
The rule
Read:
Write the multiplier under the lowest denomination of the multiplicand.
Then a remark worth discussing:
In simple numbers the scale is uniform; in compound numbers it varies with the table.
Guided practice
Together:
Multiply 2 bu. 1 pk. 1 qt. 1 pt. by 6.
How much hay in 7 loads, each weighing 10 cwt. 89 lb.?
Independent practice
Your child does problems 4 to 13.
Check and wrap-up
Answers are printed. Mental: 6 × 1 ft. 4 in.? (8 ft.)