The sum of 45 terms of A.p is 435 and the Common difference is 4. find the first team
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The first term of an AP is 5, last term is 45 and the sum is 400. Find the number of terms and the common difference.
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Correct option is A)
first term a=5, last term l=45 and S
n
= 400
Since, S
n
=
2
n
(a+l)
⇒400=
2
n
(5+45)
⇒400=
2
n
(50)
⇒400=n(25)
⇒n=16
Since, l=a+(n−1)d
⇒45=5+(16−1)d
⇒45−5=(15)d
⇒40=15d
⇒d=
15
40
⇒d=
3
8
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