Question

Coach Johnson is 10 years older than Tim. When Tim started football 3 years ago, Coach Johnson was twice his age. How old is Tim now?

Answer 1

13.

Answer 2

what you need to here is express the problem using algebra.
so we have:
1. Coach Johnson is 10 years older than Tim. Lets call Coach Johnsons age "J" and Tims age "T". So J=10+T
2. When Tim started football 3 years ago, Coach Johnson was twice his age. So 5 years ago, Coach Johnson was (J-5) years old and Tim was (T-5) years old. We therefore get (J-5)=2(T-5)

so you have these equations:

J = 10 + T
J-5 = 2(T-5)

2 equations and 2 unknowns which you should be able to solve.

Answer 3

sorry I mis-read your question, it should be 3 years ago that Tim started football NOT 5 years ago, so the equations are:

J = 10 + T
J-3 = 2(T-3)

Answer 4

if you then place the value of J from the 1st equation into the 2nd you will get:

(10+T)-3 = 2(T-3)
10+T-3=2T-6
7+T=2T-6
7+6=2T-T
13=T

Answer 5

I hope you understand how this was achieved?