Question

Sachin invested some amounts in National Saving Certificates in a specific way. In the first year, he invested  4,000 in the second year  6,000 in the third year  8,000 and so on for  12 years. Find the total amount he invested in 12 years. 

Answer 1

Sachin invested in first year = 4000

Second year investment = 6000

Third year investment = 8000

Total investment = Rs (4000 + 6000 + 8000 + .... + in 12 years)

Here,

a = 4000

d = 2000 

n = 12

Now ,

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

`"S"_12 = 12/2 [2(4000) + (12 - 1)(2000)]`

`= 6  [8000 + 22000]`

= 6 × 30000

= Rs 180000

Hence, the total amount that he invested in 12 years is Rs 180000.