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If n A.M.'s are inserted between 20 and ...

If n A.M.'s are inserted between 20 and 80 such that the ratio of first mean to the last mean is `1:3` then the value of n is

A

11

B

12

C

13

D

14

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The correct Answer is:
A
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AAKASH SERIES-SEQUENCE AND SERIES-Practice Exercise
  1. If n A.M's are inserted between two quantites a and b then their sum i...

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  2. If n A.M.'s are inserted between 4 and 96 then sum of n A.M.'s is

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  3. If n A.M.'s are inserted between 20 and 80 such that the ratio of firs...

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  4. Fifth term of G.P. is 2. The product of its first nine terms is

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  5. If (m+n)^(th) term and (m-n)^(th) terms of a G.P. are p and q respecti...

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  6. Let a(n) be the n^(th) term of G.P. If Sigma(n=1)^(100)a(2n)=alpha and...

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  7. If 4^(th), 7^(th), 10^(th) terms of a G.P. are p, q, r respectively th...

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  8. If l, m, n are the p^(th), q^(th), r^(th) terms of a G.P which are +ve...

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  9. If S=1 + a + a^(2) + ….+ oo (a lt 1) then the value of q=

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  10. If x= Sigma(n=0)^(oo) a^(n), y= Sigma(n=0)^(oo) b^(n), z= Sigma(n=0)^(...

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  11. If 3 and 2 are A.M and G.M of the roots of a quadratic equation then t...

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  12. If a,b,c are in G.P where a,b,c are positive numbers and "log"(5c)/(a)...

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  13. The arithrmetic mean of two positive numbers is 9 and geometric mean i...

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  14. If A and G are A.M and G.M between two positive numbers a and b are co...

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  15. Between 4 and 2916, (2n+1) G.M's are inserted then (n+1)^(th) G.M is

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  16. If the A.M and G.M between two numbers are in the ratio m"n then the n...

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  17. alpha, beta, gamma are the geometric means between ca, ab, ab, bc, bc,...

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  18. A square is drawn by joining the mid points of the given square a thir...

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  19. If p^(th), q^(th), r^(th) terms of a H.P be respectively a, b and c th...

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  20. If mth terms of H.P is n and nth term is m, then (m + n)th term is

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