According to the question we can form an A.P.
5000, 7000, 9000, ……
Hence, the first term a = 5000
Second term t1 = 7000
Third term t2 = 9000
Thus, common difference d = t2 – t1 = 9000 – 7000 = 2000
Here, number of terms n = 12
We need to find S12
Now, by using sum of nth term of an A.P. we will find its sum
![Maharashtra Board Solutions for Class 10 Maths Part 1 Chapter3 Maharashtra Board Solutions for Class 10 Maths Part 1 Chapter 2 - Image 25](https://cdn1.byjus.com/wp-content/uploads/2020/04/maharashtra-board-solutions-for-class-10-maths-part-1-chapter-2-image-251.png)
Where, n = no. of terms
a = first term
d = common difference
Sn = sum of n terms
Thus, on substituting the given value in formula we get,
![Maharashtra Board Solutions for Class 10 Maths Part 1 Chapter3 Maharashtra Board Solutions for Class 10 Maths Part 1 Chapter 2 - Image 26](https://cdn1.byjus.com/wp-content/uploads/2020/04/maharashtra-board-solutions-for-class-10-maths-part-1-chapter-2-image-261.png)
⇒S12 = 6 × [ 10,000 + 11 × 2000]
⇒S12 = 6 × [10,000 + 22,000]
⇒S12 = 6 × 32,000
⇒S12 = Rs. 192000