Question

In A.p first term is 5 and last te4m is 105 and sum of all term is 1155 find the number of term

Answer 1

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Given, in an AP,

a = 5
l = 105
Sn = 1155
n = ?

Then We know Sn =
$\frac{n}{2} (a + l)$

Replacing values

$1155 = \frac{n}{2} (5 + 105)$

=> n(110) = 1155(2)

=> n(55) = 1155

=> n = 21

Thus there are 21 terms in the AP.

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