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Question

The fifth and eighth terms of a geometric sequence of real numbers are 7! and 8! respectively. What is the first term?

Accepted Answer

Let the nth term of the series be ar^n-1. Because 8!7! = ar^7ar^4 = r^3 = 8, it follows that r = 2 and the first term is a = 7!r^4 = 7!16 = 315. The answer is (E).