Ray's New Practical Arithmetic · Art. 76 · Unit 8: Operations with Compound Numbers

42. Subtracting compound numbers

Goal: Your child subtracts measures with several units, borrowing by the table.

⏱ About 35 minutes · 6 steps

Open it at the Internet Archive ↗

You'll need

  • The book
  • A slate, small whiteboard or scrap paper
  • A notebook and pencil

What's in the book

Subtraction of compound numbers: a worked example with bushels and pecks, column examples for each table, and story problems 16 to 24 with printed answers.

The lesson, step by step

  1. Warm-up

    Mental: 1 bushel − 3 pecks? (1 pk.) 1 hour − 25 minutes? (35 min.)

  2. Work the book example

    Read:

    I have 67 bu. 2 pk. of wheat: how much will remain after selling 34 bu. 3 pk.?

    3 pk. can't come from 2 pk., so borrow 1 bushel = 4 pecks: 6 pk. − 3 pk. = 3 pk. Then 66 bu. − 34 bu. = 32 bu. Answer 32 bu. 3 pk.

  3. Borrowing by the table

    SayWe borrow one of the next larger unit and change it into the smaller unit: 4 pecks, 16 ounces, 60 minutes, whatever the table says.

  4. Guided practice

    Together:

    A wagon loaded with hay weighs 32 cwt. 66 lb.; the wagon alone weighs 8 cwt. 67 lb.: what is the weight of the hay?

    (23 cwt. 99 lb.)

  5. Independent practice

    Your child does several column examples and story problems 16 to 24, for example:

    If 2 bu. 1 pk. 1 qt. be taken from a bag containing 4 bushels of hickory nuts, what quantity will remain?

  6. Check and wrap-up

    Story-problem answers are printed. The column examples have no printed answers: check each by adding the answer to the smaller number. Mental: 1 lb. − 5 oz.? (11 oz.)

@teddyrookbook GitHub