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? 
:
let x = the multiplier
then
4x = original number of boys
and
5x = original number of girls
:
{{{(4x)/((5x-100))}}} = {{{6/7}}}
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