Question

what number must be added to each of a term of the ratio 7:5,so that the ratio becomes 5:4

Answer 1

so let the no. be added be x
so the according to question 

(7 + x)/(5 + x) = 5/4
28 + 4x = 25 + 5x 
x = 3

so if we add 3 to both terms we get the required answer

ie (7+3)/(5+3) = 10/8 = 5/4

Answer 2

Let the number be x
(7+x)/(5+x)=5/4
then 28=4x=25+5x
⇒ x=3
The number is 3