SOLUTION: In a school ratio of boys to girls is 4:5. when 100 girls leave the school ratio becomes 6:7. How many boys are there in the school?

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Question 726467: In a school ratio of boys to girls is 4:5. when 100 girls leave the school ratio becomes 6:7. How many boys are there in the school?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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In a school ratio of boys to girls is 4:5. when 100 girls leave the school ratio becomes 6:7.
How many boys are there in the school?
:
let x = the multiplier
then
4x = original number of boys
and
5x = original number of girls
:
%284x%29%2F%28%285x-100%29%29 = 6%2F7
Cross multiply
7(4x) = 6(5x-100)
28x = 30x - 600
600 = 30x - 28x
600 = 2x
x = 600/2
x = 300 is the multiplier
then
4(300) = 1200 boys