Answer :

By given information we can form an A.P.

5000, 7000, 9000, ……

Hence, the first term a = 5000

Second term t_{1} = 7000

Third term t_{2} = 9000

Thus, common difference d = t_{2} – t_{1} = 9000 – 7000 = 2000

Here, number of terms n = 12

We need to find S_{12}

Now, By using sum of n^{th} term of an A.P. we will find it’s sum

Where, n = no. of terms

a = first term

d = common difference

S_{n} = sum of n terms

Thus, on substituting the given value in formula we get,

⇒S_{12} = 6 × [ 10,000 + 11 × 2000]

⇒S_{12} = 6 × [10,000 + 22,000]

⇒S_{12} = 6 × 32,000

⇒S_{12} = Rs. 192000

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