Firstly the Probability can never be GREATER than 1, probability of 1 itself means that the event is sure to happen..
So choices B and C are flawed....
Of course the choices should be in some order...

Back to the question...
So we are looking at price equal to or more than 25 cents...
Only way it will be less than 25 will be when we get a nickel in each draw, so let us choose easier path with lesser calculations....
So first draw from black a will be 10/20 and the second too will be 10/20..
First draw in white urn will be 10/20 but the second will be 9/19 ..
Probability of not being able to buy... (10/20)(10/20)(10/20)(9/19)=(1/2)(1/2)(1/2)(9/19)=9/(2*2*2*19)=9/152..
So probability of buying is 1-(9/152)=143/152

A

Are we expected to know values of quarters, dimes and nickles?

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deushyant
Absolutely not . Nickel and Dime are not globally recognized US currencies .By glovally recognised i mean the currencies are not used in global transaction units

The only values you should know are "cents" and "dollars" ... This qustion seems as a self made. Choices B and C are flawed as probab9ility is never more than 1 . Please practice from GMAT trusted sources only. Use the tags for refining your question bank

A lot of words to get through, but not too hard if you take a little time to think about it.

There is only way one that she will not be able to afford a 25 cent chocolate bar: she must draw Green balls FOUR Times: two green from each urn. G-G-G-G ———> 5 + 5 + 5 + 5 = 20 cents

Any other combination of balls will allow her to buy the candy bar. The next lowest amount she could possibly get is: G-G-G-R ——-> 5 + 5 + 5 + 10 = 25 cents, which is enough.

To find the probability that she will be able to afford the candy bar, we can take:

1 - (Prob. of Unfavorable Outcome) = Prob. of Favorable Outcome


Probability of Pulling 2 Green balls from the Black urn, when the 1st ball is replaced is:

(10/20) * (10/20) = (1/2) * (1/2) = 1/4

AND

Probability of pulling 2 Green balls from the White urn when the balls are NOT replaced after taking one:

(10/20) * (9/19) = (1/2) * (9/19) = 9/38


Probability of the Unfavorable Outcome of pulling 2 green from the Black urn and pulling 2 green from the White urn therefore is = (1/4) * (9/38) = 9/152


1 - (9/152) = 143/152

(A)

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