9 coins: 7H and 2T

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April 17th 2010, 05:27 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, 05:30 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, 05:31 PM
dwsmith

$nCr*.5^n*.5^{n-r}$
April 17th 2010, 05:40 PM
Debsta

Quote:

Originally Posted by dwsmith

$nCr*.5^n*.5^{n-r}$

Check your formula!!!!
April 17th 2010, 05:40 PM
dwsmith

The book sucks don't have one. I had to find that online.
April 17th 2010, 05:43 PM
Debsta

Quote:

Originally Posted by dwsmith

The book sucks don't have one. I had to find that online.

You've either gone to a dodgy site or copied it down incorrectly. Your first power of 0.5 should be r not n.

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