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The first term of A.P. is 5, the last is...

The first term of A.P. is 5, the last is 45 and their sum is 400. If the number of terms is n and d is the common differences , then `((n)/(d))` is equal to :

A

9

B

8

C

7

D

6

Text Solution

Verified by Experts

The correct Answer is:
D
`S_(n) = (n)/(2) (a + l) rArr 400 = (n)/(2) (5 + 45) rArr n = 16`
Again , 45 = a + (n - 1) d = 5 + 15 d
`therefore d = `(40)/(15) = (8)/(3) rArr (n)/(d) = 3""((16)/(8)) = 6`
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