# By using binomial distribution if two coin are tossed 4 times ,find?

1. May 7, 2010

### mattamimi

by using binomial distribution if two coin are tossed 4 times ,find?
1)the probability of 2 heads in 4 times ?
2)the probability of less than one head once?
3)the probability of than 2 tails in 3 times ?
4)the expected number of two tails ?
5)the variance of the number of 2 heads?

Last edited by a moderator: May 8, 2010
2. May 7, 2010

### tiny-tim

Welcome to PF!

Hi mattamimi! Welcome to PF!

Show us what you've tried, and where you're stuck, and then we'll know how to help …

3. May 7, 2010

### mattamimi

thank you :)

1.) I think P(x)=4C1*(1/4)^1*(3/4)^3=0.421

4. May 7, 2010

### tiny-tim

(try using the X2 tag just above the Reply box )

uhh? that's obviously the probability of one head in 4 times

5. May 7, 2010

### mattamimi

sorry,but I couldn't solve it,can you solve the first problem

6. May 7, 2010

### tiny-tim

Sorry, but you have to do it yourself.

Please can I check that I understand 1) correctly …

is 1) asking for the probability that when 2 coins are tossed 4 times, there will be 2 heads 4 times, ie a total of 8 heads, ie all heads?

And is 2) asking for the probability that there will be 2 tails exactly once (so the other three times are either 2 heads or one of each)?

And what is the missing word in 3)?

7. May 7, 2010

### Redbelly98

Staff Emeritus
Moderator's note: thread moved from "Set Theory, Logic, Probability, Statistics"

8. May 8, 2010

### The Chaz

I think I speak for tiny-tim as well as for myself:
"YES".

Just to clarify, you are flipping two coins and recording the number of heads. Then you repeat this until you have FOUR numbers?