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Question

A person has 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, a12, are in A.P. with common difference as 2, then the time (in minutes) taken by him to count all notes, is 


Your Answer
A
24
Correct Answer
B
34
Your Answer
C
125
Your Answer
D
135

Solution

The correct option is C 34
Till 10th minute, number of notes counted =1500
 3000=n2[2(148)+(n1)(2)]
3000=n(149n)
 n2149n+3000=0
 (n125)(n24)=0
n=125 is not possible as then number of notes counted <0
n=24
Total time required =24+10=34 minutes

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