Question

Sachin invested some amount in a National Savings Certificate Scheme. In the first year, he invested ₹ 5,000; in the second year, ₹ 7,000; in the third year, ₹ 9,000, and so on. Find the total amount that he invested in 12 years.

Answer 1

Sachin invested in the first year = 5,000

Second year investment = 7,000

Third year investment = 9,000

Total investment = Rs (5,000 + 7,000 + 9,000 + .... + in 12 years)

Here,

a = 5,000

d = 2000 

n = 12

Now,

`"S"_"n" = "n"/2 [2"a" + ("n"-1)"d"]`

`"S"_12 = 12/2 [2(5,000) + (12 - 1)(2,000)]`

= 6[10,000 + 11 × 2,000]

= 6 [10,000 + 22,000]

= 6 × 32,000

= ₹ 1,92,000