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प्रश्न
The sum of A.P. 4, 7, 10, 13, ........ upto 20 terms is ______.
विकल्प
650
10 × 27
510
1300
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उत्तर
The sum of A.P. 4, 7, 10, 13, ........ upto 20 terms is 650.
Explanation:
Let a be the first term and d be the common difference of given A.P.
Then a = 4; d = 7 – 4 = 3
We know that
`S_n = n/2[2a + (n - 1)d]`
∴ `S_20 = 20/2[2 xx 4 + (20 - 1)3]`
= 10[8 + 57]
= 650
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