3. In my row in the theatre the seats are numbered consecutively from $\mathrm{T} 1$ to $\mathrm{T} 50$. I am sitting in seat T17 and you are sitting in seat T39. How many seats are there between us?
A 23
B 22
C 21
D 20
E 19
Solution
C The seats between us are numbered from T18 up to T38. So the seats between us are the 38 seats from T1 up to T38, other than the 17 seats from T1 up to T17. So there are $38-17=21$ seats between us.