How many terms of the A.P. 24, 21, 18, … must be taken so that the sum is 78 ? Explain the double answer.

In an A.P., the fourth and sixth terms are 8 and 14 respectively. Find the :

(i) first term

(ii) common difference

(iii) sum of first 20 terms

How many terms of the A.P. 25, 22, 19, …. are needed to give the sum 116 ? Also find the last term.

Find the sum of first 51 terms of the A.P. whose second and third terms are 14 and 18 respectively.