Question

What is the 25th term of the arithmetic sequence where a1=8 and a9=48 ? answers to choose from. a)113. b)118. c)123. d)128

Answer 1

128

Explanation:

Answer 2

First we need to find "d" which is difference between any 2 successive members of the sequence. Because the sequence is arithmetic that means that the difference between any 2 successive members is same and constant.

This is the formula for any member of sequence at position "n"
An = A1 + (n-1)*d
d = (a9 - a1)/(9-1)
d = 5

Now we calculate 25th member:
a25 = a1 + (25-1)*5
a25 = 128

Answer is d)