Let the three parts, which are in A .P. be a – d, a, a + d
Case I.
a – d + a + a + d = 69
⇒ 3a = 69
a = 23 ...(i)
Case II. a (a – d) = 483 ...(ii)
Putting the value of (i) in (ii), we get
23 (23 - d) = 483
Thus, the three parts are
a - d = 23 - 2 = 21
a = 23
and a + d = 23 + 2 = 25
The first and the last term of an A .P. are 4 and 81 respectively. If the common difference is 7, how many terms are there in the A .P. and what is their sum?