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If the sum (3)/(1^(2)) + (5)/(1^(2) + 2^...

If the sum `(3)/(1^(2)) + (5)/(1^(2) + 2^(2)) + (7)/(1^(2) + 2^(2) + 3^(2)) + …+` upto 20 terms is equal to `(k)/(21)`, then k is equal to

A

120

B

180

C

240

D

60

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The correct Answer is:
A
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AAKASH SERIES-SEQUENCE AND SERIES-Practice Exercise
  1. Given sum of the first n terms of an A.P is 2n+ 3n^(2). Another A.P is...

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  2. The sum (3)/(1^(2)) + (5)/(1^(2) + 2^(2)) + (7)/(1^(2)+ 2^(2) + 3^(2))...

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  3. Given a sequence of 4 numbers, first three of which are in G.P.,and th...

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  4. The value of 1^(2) + 3^(2) + 5^(2) + …+ 25^(2) is

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  5. Let a(1), a(2), a(3)….. be terms of an A.P. If (a(1) + a(2) + …..a(p))...

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  6. The sum of the series 2^(2) + 2(4^(2)) + 3(6^(2)) + ….upto 10 terms is

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  7. If S= tan^(-1) ((1)/(n^(2) +n+1)) + tan^(-1) ((1)/(n^(2) + 2n+ 3))+ …....

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  8. If a(1), a(2), a(3),…, a(n) are in A.P such that a(4) - a(7) + a(10)= ...

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  9. Given an A.P whose terms are all positive integers. The sum of its nin...

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  10. If the sum (3)/(1^(2)) + (5)/(1^(2) + 2^(2)) + (7)/(1^(2) + 2^(2) + 3^...

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  11. In a geometric progression, if the ratio of the sum of first 5 terms t...

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  12. The sum of the first 20 terms common between the series 3+7 + 11 + 15…...

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  13. Let G be the geometric mean of two positive numbers a and b, and M be ...

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  14. The lest positive integer n such that 1- (2)/(3)- (2)/(3^(2))- ….- (2)...

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  15. The number of terms in an A.P is even the sum of the odd terms in it i...

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  16. Let f(n)= [(1)/(3) + (3n)/(100)]n, where [n] denotes the greatest inte...

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  17. If the sum of first n terms of two A.P's are in the ratio 3n+8: 7n+15,...

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  18. A tree, in each year grows 5cm less than it grew in the previous year....

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  19. If log(10)2, log(10) (2^(x)-1) and log(10) (2^(x) + 3) are three conse...

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  20. If (48)/((2)(3)) + (47)/((3)(4)) + (46)/((4)(5))+ …..(2)/((48) (49)) +...

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