# tossing a fair coin

• May 10th 2010, 06:01 PM
uva123
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????
• May 10th 2010, 06:08 PM
mr fantastic
Quote:

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).
• May 10th 2010, 06:19 PM
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?
• May 10th 2010, 06:28 PM
mr fantastic
Quote:

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.
• May 10th 2010, 06:31 PM
uva123