# 9 coins: 7H and 2T

• April 17th 2010, 06:27 PM
dwsmith
9 coins: 7H and 2T
p[of tossing nine coins and getting 7H and 2T]
$9C7*.5^9*.5^2$

This equation doesn't yield the correct answer. What is wrong?
• April 17th 2010, 06:30 PM
Debsta
Quote:

Originally Posted by dwsmith
p[of tossing nine coins and getting 7H and 2T]
$9C7*.5^9*.5^2$

This equation doesn't yield the correct answer. What is wrong?

Why is 9 your first power of 0.5?
• April 17th 2010, 06:31 PM
dwsmith
$nCr*.5^n*.5^{n-r}$
• April 17th 2010, 06:40 PM
Debsta
Quote:

Originally Posted by dwsmith
$nCr*.5^n*.5^{n-r}$