Question

Raphael is twice as old as his sister is. The sum of their ages is less than 30. What is the greatest age Raphael’s sister can be?

Answer 1

let 'x' be the age of his sister
'y' be Raphael's age
y = 2x ----equation 1
x + y < 30 ----inequality 1
substitute equation 1 to the inequality
x + 2x < 30
3x < 30
x < 10
if it her age be less than 10 then the oldest she could be is x-1
x - 1 = 10 -1
= 9 yrs old