Question

C.D of an AP is -2 and first term is 80.find the sum if least term is 10?option ,A,1600,B,1620,C,1650,D,1700​

Answer 1

For the AP,

d=-2

a=80

l=10

Hence, we use the formula

$sn = \frac{n}{2} (a + l) \\ s10 = \frac{10}{2} (80 + 10) \\ s10 = 5(90) \\ s10 = 450$

Hence, sum of ten terms (all terms of the AP) is 450