SOLUTION: At the swinging club there are 3 boys for every 4 girls. How many girls are there if there are 21 boys?

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Question 1173938: At the swinging club there are 3 boys for every 4 girls. How many girls are there if there are 21 boys?
Found 2 solutions by ikleyn, greenestamps:
Answer by ikleyn(52884) About Me  (Show Source):
You can put this solution on YOUR website!
.

Use the proportion


    21_boys%2F3_boys = x_girls%2F4_girls,


or in reduced form


    21%2F3 = x%2F4.    <<<---===  the typo is just fixed at this point.


From the proportion,  find  x = %284%2A21%29%2F3 = 4*7 = 28  girls.    ANSWER

Solved.



Answer by greenestamps(13209) About Me  (Show Source):
You can put this solution on YOUR website!


The solution from the other tutor sets up the proportion as

21%2F3+=+x%2F4

and solves that equation (proportion) to find x=28.

That is of course valid. However, the problem is more easily solved by setting up the proportion as

3%2F4+=+21%2Fx

Then the problem is solved by looking at these as equivalent fractions; since 21 is 7 times 3, x has to be 7 times 4, or 28.

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Note to tutor @ikleyn --

There is currently a typo in your response (21/7 instead of 21/3)