savings are good!
Level
pending
A MAN SAVES 1OO RUPEES IN A CERTAIN YEAR AND IN EACH YEAR THEREAFTER HE SAVES 40 MORE THAN THE PRECEEDING YEAR .IN HOW MANY YEARS WILL HIS TOTAL SAVINGS AMOUNT TO RUPEES 15600??
The answer is 26.
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1 solution
We require the arithmetic series:
Σ t = 1 T 1 0 0 + 4 0 ( t − 1 ) = 6 0 T + 4 0 ( 2 T 2 + T ) = 1 5 6 0 0 ;
or T 2 + 4 T − 7 8 0 = ( T − 2 6 ) ( T + 3 0 ) = 0 ⇒ T = 2 6 , − 3 0
of which we only admit the positive value, hence T = 2 6 years.