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Formula for Sum of n Terms of an AP

The sum of th...

Question

The sum of the first 10 terms of the AP 1, 5, 9….is

A

175

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B

185

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C

190

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D

200

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Solution

The correct option is C 190
The given AP is 1, 5, 9...
first term $a$ = 1, common difference $d$ = 5-1 = 4, no. of terms $n$ = 10 and $S_{n}$ = sum of all n terms.

Now, $S_{n} = \frac{n}{2} (2 a + (n - 1) d)$

$S_{10} = \frac{10}{2} (2 \times 1 + (10 - 1) 4)$

$= 5 (2 + 36) = 190$

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