Question

Identify the 42nd term of an arithmetic sequence where a1 = -12 and a27 = 66.



70

72

111

114

Answer 1

we can get common difference d from a27
a27 = a + 26d
66 = -12 + 26*d
66+12 = 26d
26d = 78
d = 78/26 = 3

now a42 = a + 41d
= -12 + 41*3
= -12 + 123
= 111

answer is 111