A piece of equipment cost a certain factory Rs.600,000. If it depreciates in value, 15% the first, 13.5% the next year, 12% the third year, and soon. What will be its value at the end of 10 years, all percentages applying to the original cost?
Cost of equipment = 6, 00, 000
In 1 year depreciate by 15% = 6, 00, 000 * 
= 90, 000
In 2 year depreciate by 13.5% = 6, 00, 000 * 
= 81, 000
In 3 year depreciate by 12% = 6, 00, 000 * 
= 72, 000
Now A.P. is 90000, 81000, 72000,…
So, common difference = 81000 – 90000 = -9, 000
We have to find total depreciation for 10 years, Sn= 
[2a + (n – 1) d]
S10= 
[2(90, 000) + (10 – 1) -9000]
= 5 [180000 + 9 * (-9000)]
= 5 [180000 – 81000]
= 5 [99000] = 495000
Hence, cost of equipment at the end of 10 years is original cost – deprecition
= 6, 00, 000 – 4, 95, 000 = Rs. 1, 05, 000