Ray's New Practical Arithmetic · Art. 75 · Unit 8: Operations with Compound Numbers
41. Adding compound numbers
Goal: Your child adds measures with several units, carrying by the table instead of by tens.
You'll need
- The book
- A slate, small whiteboard or scrap paper
- A notebook and pencil
What's in the book
Addition of compound numbers: a worked example with bushels and pecks, the rule, remarks, column examples for each table, and story problems 18 to 26. Answers are printed for most.
The lesson, step by step
Warm-up
Mental: 3 pecks + 3 pecks? (6 pecks = 1 bu. 2 pk.) 40 min. + 30 min.? (1 hr. 10 min.)
The idea
Read:
When the numbers to be added are compound, the operation is called Addition of Compound Numbers.
Work the book's example: 25 bu. 3 pk., 14 bu. 2 pk. and the third lot. Add the pecks first; every 4 pecks make a bushel to carry.
The rule
Read:
Write the numbers to be added, placing units of the same denomination in the same column.
Write the remainder under the column added, and carry the quotient to the next column.
In writing compound numbers, if any intermediate denomination is wanting, supply its place with a cipher.
Guided practice
Do one column example from the dry measure and one from time measure together.
Independent practice
Your child does several column examples and story problems such as:
Five loads of wheat measured thus: 21 bu. 3 pk.; 14 bu. 1 pk.; 23 bu. 2 pk.; 18 bu. 1 pk.; 22 bu. 1 pk.: how many bushels in all?
Check and wrap-up
Answers are printed for the story problems (problem 18 is 100 bu.). Check column examples by adding again from the top down. Mental: 2 ft. 8 in. + 1 ft. 6 in.? (4 ft. 2 in.)
Tip
Remark 2 says it well: in plain numbers we carry for every ten; in compound numbers we carry by whatever the table says (4 pecks, 12 inches, 60 minutes).