- From a box containing 3 white balls and 7 black balls, 30 balls are drawnwith replacement.Find the probability of getting 9 and 10 white balls?

I'm having a little bit of trouble finding how to work it out any help would be much appreciated.

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- Apr 3rd 2010, 09:29 AMFunnelCan any one explain this question to me, thxs.
- From a box containing 3 white balls and 7 black balls, 30 balls are drawn

__with replacement.__Find the probability of getting 9 and 10 white balls?

I'm having a little bit of trouble finding how to work it out any help would be much appreciated. - Apr 3rd 2010, 11:22 AMArchie Meade
Hi Funnel,

this is**binomial.**

As balls are being replaced, and there are 10 balls in total, the probabilities are always

$\displaystyle P(w)=0.3,\ P(b)=0.7$

Hence, you need to calculate the binomial term for 9 whites and 21 blacks,

and seperately for 10 whites and 20 blacks

$\displaystyle \binom{30}{9}0.3^90.7^{21}$ or $\displaystyle \binom{30}{21}0.7^{21}0.3^9$

$\displaystyle \binom{30}{10}0.3^{10}0.7^{20}$ or $\displaystyle \binom{30}{20}0.7^{20}0.3^{10}$