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In the sequence 1, 2, 2, 3, 3, 3, 4, 4,4,4,....., where n consecutive terms have the value n, the 150 term isA. 17B. 16C. 18D. none of these |
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Answer» Correct Answer - A Let `150^(th)` term be equal to n. Then, `1+2+3+ . . . .+(n-1)lt150lt1+2+3+ . . . .+n` `rArr" "(n(n-1))/(2)lt150lt(n(n+1))/(2)` `rArr" "n(n-1)lt300ltn(n+1)` `rArr" "n^(2)-n-300lt0andn^(2)+n-300gt0` `rArr" "((1-sqrt(1201))/(2)ltnlt(1+sqrt(1201))/(2))` `and,(nlt(-1-sqrt(1201))/(2)orgt(-1+sqrt(1201))/(2))` `rArr" "(-16.8ltnlt17.82)and(nlt-17.82or,ngt16.8)` `rArr" "n=17`. Hence, `150^(th)` term is equal to 17. |
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