If the 2nd and 5th terms of a G.P are 6 and 48 respectively, find the sum of the first for term
-
A.
-45 -
B.
-15 -
C.
15 -
D.
33 -
E.
45
Correct Answer: Option E
Explanation
T(_{2}) = ar = 6
T(_{5}) = ar(^{4}) = 48
(frac{T_5}{T_2}) = (frac{ar^{4}}{ar}) = (frac{48}{6})
= r(^{3}) = 8
⇒ r = 2
S(_{n}) = (frac{a((r^n) – 1)}{r – 1})
S(_{4}) = (frac{a((r^4) – 1)}{r – 1})
S(_{4}) = (frac{3((2^4) – 1)}{2 – 1})
= 3(16 -1)
= 45