## Important Concepts and Formulas - Sequence and Series

Comments(42)

Anupam SG
21 Feb 2015 1:28 PM

many many thanks ,by seeing these formulaes now i able to solve each and every question of ap,gp and hp.

Bani Kumar Datta
08 Feb 2015 10:03 AM

Many thanks .I able to solve the problems of A.P & G.P now.

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

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 :

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??

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!**

reshma
27 Oct 2014 9:21 AM

what is the formula to find the product of gp

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