# Thread: Coin Tossing Problems...

1. ## Coin Tossing Problems...

Hi Everyone,

New to the forum. Terrible at math. I'm enrolled in a college Math 100 course, and I'm having some trouble understanding some concepts related to combinations, permutations, Pascal's Triangle, etc. Here are the problems I'm stuck on:

• Suppose 9 fair coins are tossed. Find the number of ways of getting exactly 6 heads.
• Find the number of ways of getting exactly 2 heads if 4 fair coins are tossed.
• A set has 6 elements. How many different subsets with 4 elements are there?

I'm not sure how to begin solving these. I don't want anyone to do my homework for me, but I'd love any help you could offer. Maybe doing one as an example, and showing me how to go about it.

Thank you all very much!
-matt

2. ## Re: Coin Tossing Problems...

Originally Posted by BackstreetZAFU
• Suppose 9 fair coins are tossed. Find the number of ways of getting exactly 6 heads.
• Find the number of ways of getting exactly 2 heads if 4 fair coins are tossed.
• A set has 6 elements. How many different subsets with 4 elements are there?
All three of these are simple combinations: $_N\mathscr{C}_k=\dbinom{N}{k}=\dfrac{N!}{k!(N-k)!}$

If we flip a coin ten times the number of exactly four heads is $_{10}\mathscr{C}_4$

SEE HERE