VedantChourey wrote:
Hi Mod's or anyone, whats wrong with this approach
I SOLVED THIS QUESTION IN THIS WAY,
6/12*5/11*6/10*5/9
First getting any 6 blue ball out of 12, then getting 5 blue ball(because its mentioned no replacement) out of 11, then getting any 6 white ball out of 10 and at last getting any 5 white ball out of 9. It gave me 5/66.
Whats wrong with this approach.
Hi
VedantChourey, I think you're on the right track if you wanted to use the probability method on this question.
However, you've only considered one case, that is Blue-White-Blue-White. You must consider all cases if you want to use this method. Keep in mind that it can be time consuming (it took me over 2min to come up with the cases and write out the formulas).
Double your first equation as the option of WWBB exists, giving us \(\frac{10}{66}\).
BWWB results in \(\frac{6}{12}*\frac{6}{11}*\frac{5}{10}*\frac{5}{9}\), giving another \(\frac{5}{66}\) or \(\frac{10}{66}\) if we consider the reverse (WBBW).
Finally, we have BWBW, which is the same formula as above, doubled to \(\frac{10}{66}\) for the reverse (WBWB).
In total, that is \(\frac{10}{66}\) three times, which gives us \(\frac{10}{66}*3=\frac{5}{11}\). Option D.
Hope that helps!