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Question

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 AP with common difference - 2, then the time taken by him to count all notes is

A
34 minutes
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B
125 minutes
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C
135 minutes
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D
24 minutes
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Solution

The correct option is A 34 minutes
Till 10th minute number of counted notes = 1500
3000=n2[2×148+(n1)(2)]=n[148n+1]n2149n+3000=0n=125,24
But n = 125 is not possible
total time = 24 + 10 = 34 minutes.

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