QuestionJAMBGeneral Maths1988ObjectiveSequences & series (AP, GP)Sequences & series (AP, GP)
If 7 and 189 are the first and fourth terms of a geometric progression respectively, find the sum of the first three terms.
Worked solution (try it first)
The 4th term of a G.P. is
ar3, so
7r3=189 and
r3=27.
Take the cube root:
r=3.
The first three terms are 7, 21 and 63, and their sum is 91, option B.
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