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Question
Shubhankar invested in a national savings certificate scheme. In the first year he invested ₹ 500, in the second year ₹ 700, in the third year ₹ 900 and so on. Find the total amount that he invested in 12 years.
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Solution
Amount invested by Shubhankar in the national savings certificate scheme is as follows:
500, 700, 900,...
The above sequence is an A.P.
∴ a = 500, d = 700 – 500 = 200, n = 12
Now, `S_n = n/2 [2a + (n - 1)d]`
∴ `S_12 = 12/2 [2(500) + (12 - 1)(200)]`
= 6[1000 + 11(200)]
= 6(1000 + 2200)
= 6(3200)
= 19200
∴ The total amount invested by Shubhankar is ₹ 19,200.
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