The 6th term of a G.P is -2 and its first term is 18. What is the common ratio?
- A.
–^{1}/_{2} - B.
-1/3 - C.
1/4 - D.
2 - E.
3
Correct Answer: Option B
Explanation
a, ar, ar^{2}, ar^{3}, ar^{4}, ar^{5}
6th term = ar^{5} = ^{2}/_{27}
1st term = a = 18
=> ar^{5} = 18r^{5} = ^{2}/_{27}
r^{5} =
-218 x 27
=
-19 x 27
r^{5} =
-1243
√r^{5} = 5√^{-1}/_{243}
= -1/3