Question

A man arranges to pay off a depth of rupees 3600 by 40 annul installments which from an arthemetic series .When 30 of the installments are paid he dies leaving of first installment

Answer 1

first installment = a

common difference between any two consecutive installments =d

Using the formula for the sum of an A.P.

S=n/2 [2a+(n−1)d]

3600=40/2 [2a+(40−1)d]

180= 2a+39d

And 

2400=30/2 [2a+(30−1)d]

160=2a+29d

On solving The above equations we get

d=2 and a=51

Value of 8th installment= 51+(8−1)2 = Rs 65

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