I get confused with the following question.
“9 different books are to be arranged on a bookshelf. 3 of these books were written by Charles Dickens. How many possible permutations are there if the books by Dickens are separated from each other?”
Thank you very much, Sir.
I’ve always loved ur site, I’ve recommended it to each of my friends. I love how u show something beautiful in math hidden from the textbooks, its like sherlock explaining his reasoning after a mess of confusion. Like sudden light in darkness, that aha moment, I love it.
However, this post is disappointing. Many textbooks offer this same explanation and its not helpful. Usually u get down to the level of the reader, assuming he cannot think math, and explain math in terms of common sense. U always write the article after getting urself a golden aha moment. Here, u didn’t do that. U assumed all readers are familiar with how the number of choices multiply (7x6x5), which is not the case. Or perhaps u urself has not felt that aha moment in permutation and combinations.
Sorry for my harsh words. I trust ur website so much and wanted this article badly. But its very disappointing.
thanks kalid. yo explanations helped me a lot to find out permutations easy.
thanks again.
So brilliant! It really helps you giving a tutorials like this to people that learn differently. I am partially dyslexic and now I am understanding maths VERY well! I have become a kind of go to person in some respects for some problems in math thanks to you. 
@Kloh: Glad you enjoyed it! Very close with a few corrections.
Of the 8! (40,320) ways to arrange 8 objects, there are 8!/(8-3)! = 876 = 336 starting triplets. For each triplet there are then 40,320/336 = 120 options afterwards. Note that 120 is 5!, or the ways to re-arrange the remaining elements.
@Pyae: Thanks!
@Abarajithan: Thanks for the feedback! Check out http://betterexplained.com/articles/how-to-understand-combinations-using-multiplication/ for more on why we multiply. As a quick check, imagine you have 3 shirts and 4 pants. How many outfits can you make? (Would it be 3 + 4 or 3 x 4?). Now, imagine you have 3 shirts, 4 pants, and 5 hats. How many outfits can you make? (3 + 4 + 5 or 3 x 4 x 5?). Hope that helps.
@melani, @josh: Thanks!
I really like your style!! The way u turned this scary topic into fun by magic u should definitely write a book. Cause your style is just what most kids need right now. I’m serious. No joking.
i Wonder how you became soo good??? i study but make mistakes at the examnation room
I AM SO CONFUSED
How many arrangements can be formed of word"Equation" if all the vowels are kept together?
Great site!
I have a question:
A choir consist of 13 sopranos,12 altos,6 tenors,7 basses.A group consisting of 10 sopranos, 9 altos,4 tenors and 4 basses is to be chosen from the choir.
1-In how many ways can the group be chosen?
2-In how many ways can the 10 chosen sopranos be arranged in a line if the 6 tallest stand next to each other?
3-The 4 tenors and 4 basses in the group stand in a single line with all the tenors next to each other and all the basses next to each other.How many possible arrangements are there if three of the tenors refuse to stnd next to any of the basses?
Desperately waiting for an explanation…I firmly believe that understanding the explanation of this question would help me understand this topic even more…!!
really better explained…
it was really a good experience
1.find the number of diagonals that can be drawn by joining the angular point of octagon?
2.A man has 7 relatives,4 of them are ladies and 3 gentlemen,his wife has 7 relatives and 3 of them are ladies and 4 gentlemen.In how many ways Can they invite a dinner party of 3 ladies and 4 gentlemen so that there are 3 of men’s relatives and 3 of wife’s relatives?
plssssss answer me these two questions…its really irritating me…
i have two unequal lists of data, which are scattered through a list that is longer than either. So there are three possibilities A, B or nothing. How do I calculate the probability of A and B being on the same line ?
Another great explanation Kalid.
Thank you so much sir for such a lucid explanation.
This part is in our microbiology & as I didn’t have maths in 12th I was finding rather difficult to cope up with all this…
Please can you give me detail explanation with reference to binomial, Poisson’s and normal distribution… I’ll be very grateful to you sir.
This was very very very helpful. Finally, I get it.
pls sir, How many different circles can be drawn each of which passes through 3 of the 5 points a,b,c,d,e.if no.3 of the points are Collinear and no.4 are concyclic?..