Question

5.
The first term of an A.P. is 5 and the last term is 45. If the sum of all the terms is 400, the number of terms is​

Answer 1

Answer:

Given that, Sn=400, An= 45 and a=5

An=45

a+(n-1)d=45

(n-1)d=40

And,Sn=400

n/2{2a+(n-1)d}=400

n{2a+(n-1)d}=800

n{2×5+40}=800 {As a=5,(n-1)d=40}

n=800/50=16 =Number of terms

And,we have

(n-1)d=40

d=40/15=2.67=Common Difference

Step-by-step explanation:

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