Math miscellaneousEasy
Question
The sum of the 3rd and the 4th terms of a G.P. is 60 and the product of its first three terms is 1000. If the first term of this G.P. is positive, then its 7th term is :
Options
A.7290
B.640
C.2430
D.320
Solution
a(ar)(ar2) = 1000 ⇒ ar = 10
and ar2 + ar3 = 60 ⇒ ar(r + r2) = 60
⇒ r2 + r – 6 = 0
r = 2, − 3
a = 5, a = − 10/3(reject)
T7 = ar6 = 5(2)6 = 5 × 64 = 320
and ar2 + ar3 = 60 ⇒ ar(r + r2) = 60
⇒ r2 + r – 6 = 0
r = 2, − 3
a = 5, a = − 10/3(reject)
T7 = ar6 = 5(2)6 = 5 × 64 = 320
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