Mareo is twice as old as his friend Peter. Peter is 5years olderthan Alice. In 5years John will be three times as old as Alice. How old is Peter now?

Answer 1

M=2P
P=5+A
J+5=3(A+5)

So you have J, A, P, M as unknowns, and three statements. You can't solve all with a unique solution.

One of many solutions could be
P=10
A=5
M=20
J=25