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If the sum of the first `2n`terms of the A.P. 2, 5, 8, ..., is equal to the sum of the first `n`terms of A.P. 57, 59, 61, ..., then `n`equals`10`b. `12`c. `11`d. `13`A. 10B. 12C. 11D. 13 |
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Answer» Correct Answer - C According to given condition, `rArr (2n)/(2) [2 xx 2 + (2n -1) xx 3] = (n)/(2) [2 xx 57 + (n -1) xx 2]` `rArr (4 + 6n - 3) = (1)/(2) (114 + 2n -2)` `rArr 6n += 57 + n -1 rArr 5n = 55` `:. N = 11` |
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