A man is employed to count ₹ 10710 . He counts at the rate of 180 per minute for half an hour. After this he counts at the rate of ₹3 less every minute than the preceding minute. Find the time taken by him to count the entire amount.

Solution:

Given that the amount to be counted is ₹ 10710
We have to find the time taken by man to count the entire amount.
He counts the amount at the rate of ₹ 180 per minute for 30 minutes.
Amount to be counted in an hour ₹ 5400
Amount left ₹ 5310

Rate of counting is decreases at ₹ 3 per minute after an hour. This rate will form an A.P.
A.P. is
Here and
Using the formula,


Consider the value of As, at min he will count ₹ 0
As a result, the total time taken by him to count the entire amount minutes.