The first five terms of an arithmetic sequence are 20
1
4
7
10
13
Write down an expression, in terms of n, for the nth term of this sequence.

At the beginning of 1974/75,2 years a man invested #2000 in a bank at 12.5% compound interest, if it degree #650 at the end of each two years to pay his son's school fees, after payment of interest to pay his son's school fees, how much did he have left at the beginning of the 1978/79 school year?