problem:
You can buy 6 cakes at the supermarket A for $ 12.40.
You can buy 5 of the same cakes at the supermarket B for $ 11.20
Which place is the better buy?
answer:
1. step: proportion
supermarket A
: 6 cakes – 12.40 $
* 1 cake – x $
supermarket B
: 5 cakes – 11.20 $
* 1 cake – x $
2. step: which proportion?
↓less cakes ↓less $ = directly proportional for both
3. step: formula
supermarket A supermarket B
x = 12.40 * 1 x = 11.20 * 1
6 5
x = 2.07 $ x = 2.24 $
4. step: answer
Supermarket A is the better buy.