Mark is 11 years older than his sister. In 8 years he will be twice as old as she will be then. How old are they now?

Answer 1

M = S+11
M+8 = 2*(S+8) = 2*S + 16
Now solve
M = 2S+8
2S+8 = S+11
S = 3
M = 14

Answer 2

T=25+R
R=25-5=20
20+25=45
T=45
R=20

Answer 3

Bob is 8 years older than his sister. 3 years ago he was 3 times older than his sister. How old are they both?