Question

the sum of the two number is 30 and their difference is 12 .find the ratio of these two no

Answer 1

Let the numbers be 'x' and 'y' 
x+y=30-------(1)
x-y=12--------(2)
Add (1) and (2),
2x=42
x=21
Substitute the value of x in eq(1)
21+y=30
y=30-21
y=9.
Their ratio=x/y=21/9=7/3.

Answer 2

let the number be x and y
  given, 
           x+y=30     --- (1)
           x-y=12      ---(2)
on adding equation (1) and (2) we get,
x+y+x-y=30+12
x+x=42
2x=42
x=42/2
x=21
after putting the value of x in (1) equation,
21+y=30                      (x+y=30)
y=30-21
y=9
 
the ratio of these two number,
=21:9
=7:3