I am a beginner here and have recently started learning Discrete math. I dont know how to solve the following question.

Please help.

Q. Let A ={0,1,2,3} and B ={0,1,2}. How many functions are there from A to B that are onto?

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- Oct 2nd 2010, 03:02 PMhimanshugptNumber of Onto Function between two sets?
I am a beginner here and have recently started learning Discrete math. I dont know how to solve the following question.

Please help.

**Q. Let A ={0,1,2,3} and B ={0,1,2}. How many functions are there from A to B that are onto?** - Oct 2nd 2010, 03:33 PMPlato
I will answer this question for the finite case only.

Being beginner, you may not understand the reply.

You need to know how to use the generalized*inclusion/exclusion rule*.

Let denote the number of elements in set .

If**there are no onto**functions .

If then number of onto functions is given by:

. - Oct 2nd 2010, 03:37 PMhimanshugpt
Thanks for the reply Plato.

Is there any link or topic I have to ponder on to understand this.

I am unable to get what the variablemean in the above formula.*j* - Oct 2nd 2010, 03:49 PMPlato
Well, I did say that you may not have any idea what is going on.

It is rather advanced material. Here is webpage on inclusion/exclusion.

In essence we are selecting elements of to be included then excluded. - Oct 2nd 2010, 03:51 PMhimanshugpt
Thanks for the Link. I will try to understand this and will post here if I encounter any other problem.

Thanks again. :)