Properties of Numbers

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Fractional Parts
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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 the napkins = 3/3
- all the napkins = 1/3
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left to be folded = 2/3

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.

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