Question

Find the 60th60th term of the ap 8, 10, 12, ., if it has a total of 60 terms and hence find the sum of its last 10 terms

Answer 1

a = 8

d = 10 - 8
= 2

$t_{60} = a + 59d \\ \\ = 8 + 59 \times 2 \\ \\ = 8 + 118 \\ \\ = 126$



$S_{10} = \frac{n}{2} \times {2a \: +(n - 1)d } \\ \\ = \frac{10}{2} \times 2 \times 8 + (10 - 1)2 \\ \\ = 5 \times 16 + 9 \times 2 \\ \\ = 5 \times 16 + 18 \\ \\ = 80 + 18 \\ \\ = 98$