Ray's New Practical Arithmetic · Art. 173 · Unit 15: Applications of Percentage: Mercantile Transactions
81. Trade discount
Goal: Your child finds the price after one or more successive discounts and works backward to a list price.
You'll need
- Paper and pencil, or a slate or small whiteboard
What's in the book
Page 208 defines Trade Discount (Art. 173). Page 209 explains successive discounts like "20 and 5 off" and gives examples 1–7 with printed answers.
The lesson, step by step
Warm-up
Ask: A $20 book is 10% off. What do you pay? Now take another 10% off that price. Is that the same as 20% off?
The idea
A list, or regular, price is an established price, assumed by the seller as a basis upon which to calculate discounts.
The discount is the deduction from the list, or regular, price.
Successive discounts are taken one after another: "20 and 5 off" means 20% off the price, then 5% off what is left.
Work an example together
A bill of goods amounted to $225.50 list; 20% off being allowed, what was paid for the goods?
$225.50 × .80 = $180.40.
Guided practice
Do these together:
I paid $1430.75 for a lot of groceries, which was 3% discount from the face of the bill: what was the amount of the bill?
A bill of goods cost $390.45 at 25 and 5 off: what was the list price?
For the second, $390.45 is .75 × .95 of the list price, so divide by .7125.
Independent practice and check
Your child works the other examples on page 209. 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: $100 less 10 and 10 off (= $81); $50 less 20% off; $40 less 25 off.
Tip
Old business note: "for cash" meant paying as soon as the goods arrived, and "time purchases" meant paying some months later. A small extra discount for cash was common.