The sum of the first n terms of an AP is 400. If the sum of the first and last term is 20, then the value of n will be .

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Solution

The correct option is B 40
For an AP series, we know that the sum of the first n terms is given by;
$S u m = \frac{n}{2} [F i r s t t e r m + L a s t t e r m]$

We are given that sum = 400 and $[F i r s t t e r m + L a s t t e r m] = 20$

On substituting the values, we see that
$400 = \frac{n}{2} \times 20$
On further simplification, we get
$20 = \frac{n}{2}$
Therefore, $n = 40$ .

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The sum of the first n terms of an AP is 400. If the sum of the first and last term is 20, then the value of n will be .

The correct option is B 40For an AP series, we know that the sum of the first n terms is given by; Sum=n2[First term+Last term] We are given that sum = 400 and [First term+Last term]=20 On substituting the values, we see that 400=n2×20 On further simplification, we get 20=n2 Therefore, n=40.