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Re: A certain tin contains exactly 10 identically shaped gumdrop [#permalink]
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Expert Reply
kunalkmr62 wrote:
We also need to calculate the probability of selecting the 1st gumdrop , which will be 1/5 for any gumdeop and then multiply the probability of selecting the 2nd gumdrop , which should be 1/9.
To make it clear would you have also ignored the probability of selecting the 1st gumdrop if the numbers would have been different ?



No...

You can choose any of the first so 10/10, the second has to be a pair of this so1/9
Total 10/10*(1/9)=1/9..

If we take the way you have taken..
Then you are calculating ways to pick up a specific gumdeop..
So (2/10)*(1/9)...
But the one you choose can be any of five so 5C1..
So 5C1*(1/5)(1/9)=5*(1/5)(1/9)=1/9
Same answer
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Re: A certain tin contains exactly 10 identically shaped gumdrop [#permalink]
1
To select first gumdrop we have 10 choices that means 10C1/10C1

for second one we will be having 1C1 / 9C1

therefore, (10C1/10C1) * (1C1 / 9C1)
1 * 1/9

So answer is 1/9
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Re: A certain tin contains exactly 10 identically shaped gumdrop [#permalink]
1
Probability of selecting first gumdrop = 2/10

Probability of selecting gumdrop with same flavour the second time = 1/9

Probability of selecting one of five gumdrops 5C1 = 5

Therefore

2/10 x 1/9 x 5 = 1/9.

Answer C

Adewale Fasipe, quant instructor from Lagos Nigeria.
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