Fractional Parts

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:

3 out of 4 equals how much out of 100 -- 3 times 100 divided by 4

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 3/3 of the napkins minus 1/3 (already folded) shows that two-thirds of them left.


two-thirds of the 60 napkins are left to be folded.  2 times 60 divided by 3 equals 40 napkins left.




Jack's rent is two-fifths of his income.   If he earns $1500, how much is his rent?

Jack earns $1500 and pays two-fifths of it for rent.  2 times 1500 divided by 5 equals &600 rent.




PRACTICE QUESTIONS:

1)   Tom broke one-sixth of a dozen eggs. How many eggs are not broken?
2)   Kim ate one-fourth of sixty mints.   How many mints are left?
3)   Pam painted three-fourths of the tiles.   How many of the 80 tiles are painted?
4)   Dale sold one-eighth of the books.   How many of the 40 books are left?



ANSWERS:

1)   10 eggs are UNBROKEN     2)   45 are left     3)   60 are painted     4)   35 are left




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