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

A person has to count 4500 currency notes. Let an denote the number of

1.	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
Answer» A person has to count $4500$ currency notes. Let $a_{n}$ denote the number of notes he counts in the $n^{th}$ minute. If $a_{1} = a_{2} = \dots = a_{10} = 150$ and $a_{10}, a_{11}, a_{12}, \dots$ are in A.P. with common difference as $- 2$ , then the time (in minutes) taken by him to count all notes, is