If a certain number is added to the numerator and denominator of 5/11, the result is 7/10. find the number.

Let's represent the number by x.

x+5/x+11=7/10 (cross multiply) 9+5/9+11=14/20=7/10

(x+5) * 10 = (x+11) * 7

10x+50=7x+77

10x+50-50=7x+77-50

10x=7x+27

10x-7x=27

3x=27

3x/3=27/3

x=9

therefore the number is 9