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

The first term of an A.P. is 5, the last term is 45 and sum is 400. Find the number of terms and the common difference.

Text Solution

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`" "a = 5`
`" "a_n = 45`
`" "S_n = 400`
`rArr (n)/(2) (5+ 45) = 400`
`50 n = 800`
`n = 16`
also `a_n = 45`
`5 + 15 d = 45`
` 15 d = 40`
`d= 8//3`
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Knowledge Check

  • 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
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    6

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