# Thread: tossing a fair coin

1. ## tossing a fair coin

Suppose that a fair coin is tossed repeatedly until a head is obtained for the first time.

(a) What is the expected number of tosses that will be required?
(b) What is the expected number of tails that will be obtained before the first head is
obtained?

does anyone know how to do this one????

2. Originally Posted by uva123
Suppose that a fair coin is tossed repeatedly until a head is obtained for the first time.

(a) What is the expected number of tosses that will be required?
(b) What is the expected number of tails that will be obtained before the first head is
obtained?

does anyone know how to do this one????
The answer to (b) is one less than the answer to (a). Review the geometric distribution to get the answer to (a).

3. i found E(x) in (a) to equal 2 and so (b) would equal 1 but i wasnt sure that was correct. is that what you found?

4. Originally Posted by uva123
i found E(x) in (a) to equal 2 and so (b) would equal 1 but i wasnt sure that was correct. is that what you found?
Yes.

5. thanks for all your help!!