JEE Main 2020 — Sequences And Series Question with Solution
From: JEE Main 2020 (Online) 5th September Evening Slot
Question
If the sum of the second, third and fourth terms
of a positive term G.P. is 3 and the sum of its
sixth, seventh and eighth terms is 243, then the
sum of the first 50 terms of this G.P. is :
Choose an option
Show full solutionCorrect option: D
Correct answer
D
Step-by-step explanation
Let first term = a > 0
Common ratio = r > 0
ar + ar2 + ar3 = 3 ....(i)
ar5 + ar6 + ar7 = 243 ....(ii)
r4(ar + ar2 + ar3) = 243
r4(3) = 243
r = 3 as r > 0
from (i)
3a + 9a + 27a = 3
a =
S50 =
=
Common ratio = r > 0
ar + ar2 + ar3 = 3 ....(i)
ar5 + ar6 + ar7 = 243 ....(ii)
r4(ar + ar2 + ar3) = 243
r4(3) = 243
r = 3 as r > 0
from (i)
3a + 9a + 27a = 3
a =
S50 =
=
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