Question

the difference between the ages of the sisters is 10 years,. if 15 years ago, the elder one was twice as old as the the younger one, find their present age.

Answer 1

Let the older one's age be x,the younger's y.
We know,
x-y=10--------(1)

Also,
x-15 = 2(y-15)

Which Simplifies to
x-2y = -15------(2)

Solving (1) and (2),

x-y=10
x-2y=-15
-------------
y=25

Therefore x=35



Hope that helped!
^_^

Answer 2

let,
x-age of elder sister
y-age of younger sister
x-y=10
x-15=2 (y-15)
here you have two equations
x-15=2y-30
x-2y= -15
x-y=10
if you subtract them you will get
-y= -25
y=25
x=35