1.
How many terms are there in 20, 25, 30......... 140

2.
Find the first term of an AP whose 8th and 12th terms are respectively 39 and 59.

4.
The sum of the first 16 terms of an AP whose first term and third term are 5 and 15 respectively is

5.
How many terms are there in the GP 5, 20, 80, 320........... 20480?