Calulate chance to get x heads in y flips

[zeion]

Homework Statement

So if I wanted to get the chance to get x heads in y flips (x <= y)
I use y choose x / 2^y right?

Homework Equations

The Attempt at a Solution

 

[vela]

For a fair coin, yes.

 

[skeptic2]

So the chance of getting 10 heads with 5 flips is 0.3125? ;-)

 

[Mark44]

So the chance of getting 10 heads with 5 flips is 0.3125? ;-)

See below.

So if I wanted to get the chance to get x heads in y flips (x <= y)[/color]
I use y choose x / 2^y right?

 

[zeion]

I win.