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प्रश्न
The sum of 40 terms of the A.P. 7 + 10 + 13 + 16 + .......... is ______.
विकल्प
5240
2620
1310
2680
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उत्तर
The sum of 40 terms of the A.P. 7 + 10 + 13 + 16 + .......... is 2620.
Explanation:
For given A.P, a = 7; d = 10 – 7 = 3
We know that
`S_n = n/2 [2a + (n - 1)d]`
∴ `S_40 = 40/2 [2 xx 7 + (40 - 1)3]`
= 20[14 + 117]
= 20 × 131
= 2620
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