sum(83) = (first + last)/2
22327 = 83(23 + last)/2
269 = (23+last)/2
538 = 23+last
last = 515
or, the long way
sum(83) = (83/2)(2a + 82d)
22327*2 = 83(46 + 82d)
538 = 46+82d
d = 6
term(83) = a + 82d
= 23 + 82(6) = 515
The sum of all 83 terms of an A.P. is 22327 . If the first term of the A.P. is 23 , then what is its last term ?
1 answer