## Important Concepts and Formulas - Sequence and Series

vishal 17 Dec 2014 7:25 PM
Divide 20 into 4 parts which are in A.P. and such that the product of first and fourth is to product of the second and third in ratio 2:3

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Jay 20 Dec 2014 11:15 PM
2,4,6,8  or 8,6,4,2

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Tanika monga 08 Dec 2014 2:26 PM
If (m+n) & (m-n) are in gp & respectively p & q then find the value of m :
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priya 16 Nov 2014 7:13 PM
In how many ways can letters of English alphabet be arranged so that there are 7 letters between the letters a and b and no letter is repeated??
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Raj 21 Nov 2014 12:37 AM
Assuming that all arrangements are done by taking all 26 alphabets at a time

Removing A and B, there are 24 letters. From these letters, 7 alphabets can be arranged between A and B in 24P7 ways

A and B can be arranged in 2! ways

Remaining alphabets = 17
Consider (A)(7 letters)(B) as a single alphabet now
Lets consider this as a total of 18  alphabets . These alphabets can be arranged among themselves in 18! ways

Required number of ways = 24P7* 2! * 18!
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reshma 27 Oct 2014 9:21 AM
what is the formula to find the product of gp
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ravinder 21 Nov 2014 4:55 AM
a raise to power n multiply r raise to power n(n+1)/2
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PARVEEN 18 Oct 2014 4:09 PM
sum of three numbers in ap is 21 and if one addes to third no and one deducted from 2nd no the series become gp what are the numbers
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Raj 23 Oct 2014 10:31 PM
Let numbers be (a-d), a and (a+d)

sum = 3a = 21
a = 7

So the numbers are (7-d), 7 , (7+d)

Given that (7-d), 6, (8+d) are in GP
62 = (7-d)(8+d)
36 = 56 + 7d - 8d -d2
d2 + d - 20 = 0
(d+5)(d-4)=0
d = -5 or 4

so numbers are 12, 7, 2
OR
numbers are 3, 7, 11

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vivek 11 Oct 2014 11:42 AM
what is answer for this question
if the 9th term ap is zero then t29/t19=k. where k=?
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