Rony, who is sixteen years old, is four times as old as his sister. How old will Rony be when he is twice as old as his sister?
Now Rony is 16 years old
Sister is 16 / 4 = 4 years old
After x years Rony will be 16 + x
yeras old
Sister will be 4 + x years old
Now you must solve equation :
( 16 + x ) / ( 4 + x ) = 2 Multiply both sides by 4 + x
16 + x = 2 ( 4 + x )
16 + x = 8 + 2 x Subtract 8 to both sides
16 + x - 8 = 8 + 2 x - 8
8 + x = 2 x Subtract x to both sides
8 + x - x = 2 x - x
8 = x
x = 8
After 8 years Ronny will be 16 + 8 = 24 years old
Sister will be 4 + 8 = 12 years old
24 / 12 = 2