The sum of some terms of G.P. is 315 whose first term and the common ratio are 5 and 2, respectively. Find the last term and the number of terms.
Let the sum of n terms of the G.P. be 315.
It is known that, 
It is given that the first term a is 5 and common ratio r is 2.
∴Last term of the G.P = 6th term = ar6 – 1 = (5)(2)5 = (5)(32) = 160
Thus, the last term of the G.P. is 160.
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