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  • 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 Option: 1 20 Option: 2 8 Option: 3 10 Option: 4</s

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
Option: 1 20
Option: 2 8
Option: 3 10
Option: 4 16

Answers (1)

First term (a)=  5

last term (l) = 45

\\S_n = \frac{n}{2}(a+l) \\ 400 = \frac{n}{2}(5+45) \\ n = 16

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