Question

find the sum of 10 terms of AP 2,5,8,11,...
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Answer 1

Answer:

S10=n/2(2a+(n-1)d

=10/2(2*2+(10-1)3

=5(4+9(3))

=5(4+27)

=5(31)

=155

sum of 10terms is 155

Answer 2

Given:

An AP: 2, 5, 8, 11,...

To Find:

Sum of the first 10 terms of the AP.

Solution:

We are given the AP 2, 5, 8, 11,...

The sum of the first $n$ terms of an AP can be given by

$S_n=\frac{n}{2} [2a+(n-1)d]$

where $a$ is the first term of the AP & $d$ is its common difference i.e. difference between any two consecutive terms.

Here, the common difference of the AP, $d=3$

Sum of first 10 terms

    $S_{10}=\frac{10}{2} [2*2+(10-1)3]$

⇒ $S_{10}=5 [4+27]$

⇒ $S_{10}=155$

Hence, the sum of the first 10 terms of the given AP is equal to 155.

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