Question

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

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Answer 1

n=16 and d=8/3

first term a =5 last term 12 45 and Sn =400

Since, Sn=n/2(a+1)

400=n/2 (5+45)

400=n/2(50)

400 =n/2(50)

409n(25)

n=16

Since 1=a+(n-1)d

45=5+(16/1)d

45-5=(15)d

40=15d

d=40/15

d 28/3

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