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Re: A certain candy store sells jellybeans in the following six [#permalink]
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Please provide a short method.
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Re: A certain candy store sells jellybeans in the following six [#permalink]
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chetan2u wrote:
AE wrote:
Please provide a short method.

Carcass wrote:
A certain candy store sells jellybeans in the following six flavors only: banana, chocolate, grape, lemon, peach and strawberry. The jellybeans are sorted into boxes containing exactly 2, 3 or 4 different flavors, with each possible assortment of flavors appearing in exactly one box. What is the probability that any given box contains grape jellybeans?

A. \(\frac{1}{6}\)

B. \(\frac{1}{3}\)

C. \(\frac{2}{5}\)

D. \(\frac{1}{2}\)

E. \(\frac{3}{4}\)


Let us choose that none are grape jellybeans..
1) when the box contains 2 flavours -
total ways - \(T_1=6C2=15\) and without jelly beans - \(W_1=5C2=10\)
2) when the box contains 3 flavours -
total ways - \(T_2=6C3=20\) and without jelly beans - \(W_2=5C3=10\)
3) when the box contains 4 flavours -
total ways - \(T_2=6C4=15\) and without jelly beans - \(W_2=5C4=5\)

Probability that jelly is not there = \(\frac{W_1+W_2+W_3}{T_1+T_2+T_3}=\frac{10+10+5}{15+20+15}=\frac{25}{50}=\frac{1}{2}\)
so Probability that jelly is there = \(1-\frac{1}{2}=\frac{1}{2}\)

D


This explanation was amazing! A real Eye opener!
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Re: A certain candy store sells jellybeans in the following six [#permalink]
Can you explain why we are solving it through 1-P (atleast scenario) method?
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Re: A certain candy store sells jellybeans in the following six [#permalink]
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kanny wrote:
Can you explain why we are solving it through 1-P (atleast scenario) method?


The solution by @pranab223 uses the complement (i.e, the probability of selecting a box with grape flavor = 1 - the probability of NOT selecting a box with grape flavor)

Cheers,
Brent
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Re: A certain candy store sells jellybeans in the following six [#permalink]
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There is ambiguity in this question, it is said that each of the flavor appears in exactly one box. So it can be understood as 3 boxes with 2 flavors each or 2 boxes with three flavors each or 2 boxes with 4 flavors in one and 2 flavors in another.
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Re: A certain candy store sells jellybeans in the following six [#permalink]
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kanny wrote:
Can you explain why we are solving it through 1-P (atleast scenario) method?


You could also do it through the straightforward method by counting 5C1 + 5C2 + 5C3 (Number of selections of the other flavors needed to complete each assortment containing a grape). You will arrive at the same result. You might have noticed that each flavor is used exactly half the total number of assortments. Might help to gain some time on similar questions.
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Re: A certain candy store sells jellybeans in the following six [#permalink]
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