A person is to count 4500 currency notes. Let an denote the number of notes he counts in the nth minute. If a1 = a2 = … = a10 = 150 and a10, a11, … are in an A.P. with common difference –2, then the time taken by him to count all the notes is

# A person is to count $4500$ currency notes. Let an denote the number of notes he counts in the nth minute. If  and  are in an A.P. with common difference $–2$, then the time taken by him to count all the notes is

1. A

$125$ minutes

2. B

$135$minutes

3. C

$24$ minutes

4. D

$34$ minutes

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### Solution:

Suppose he takes $n$ minutes to count $4500$ notes. We have  and  is an A.P. with common difference $d=-2.$
We are given

All the notes get counted in $34$ minutes.

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