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

[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?

 

[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 …

start with 1). ​

 

[mattamimi]

thank you :)


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

 

[tiny-tim]

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

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

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

 

[mattamimi]

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

 

[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)?

 

[Redbelly98]

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

 

[The Chaz]

...can you solve the first problem

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?