If you spend one-fourth of a dollar, how much is left?
First divide the dollar into four equal pieces (the denominator -- bottom number
-- tells how many equal pieces are in each whole thing). 100
÷ 4 = 25. That's the amount used.
What was the question? How much of the dollar is left?
You can set-up and solve this type of question as a proportion:
Use cross-products to solve: 3 times 100 = 4 times (the missing part)
|
3 times
100 |
= |
4 times
the amount left
|
| 300 |
= |
4 times
the amount left
|
| 300/4 |
= |
4/4 times
the amount left
|
| 75 (cents) |
= |
the amount left
|
Notice that the answer will be for whatever question you asked --the set-up
can save you an extra step later (or save you from forgetting that there
was a second step).
You fold one-third of sixty napkins. How many are left?
all the napkins = 3/3
- all the napkins = 1/3
-------------------------------------------
left to be folded = 2/3
Jack's rent is two-fifths of his income. If he earns $1500, how
much is his rent?
 | 
