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The waiter at an expensive restaurant has noticed that 60% [#permalink]

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03 Apr 2013, 18:06

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The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

Re: The waiter at an expensive resturant has noticed [#permalink]

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03 Apr 2013, 21:27

Tagger wrote:

The waiter at an expensive resturant has noticed that 60% of the couples order desert and coffee. However, 20% of the couples who order desert dont order coffee. what is the probability that the next couple the waiter seats will not order desert?

A.) 20% B.) 25% C.) 40% D.) 60% E.) 75%

Let the number of people ordering only desert = d, only ordering coffee be c and ordering both be b. Given that , 20 % of (b+d) = d

or 4d = b.

Thus, as b = 60, d = 15. The total number of people not ordering desert = 100-(60+15) = 25.

The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20% B. 25% C. 40% D. 60% E. 75%

Probably the best way to solve this question is using the double set matrix, as shown below:

Attachment:

Coffee and Dessert.png [ 3.79 KiB | Viewed 8467 times ]

From above, we have that 60+0.2x=x --> x=75.

Thus, the probability that the next couple will not order dessert (yellow box) is 100-75=25.

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

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17 Aug 2013, 22:25

Solving for X in the figure shown below we will get Couples for deserts as 75% And couples not ordering deserts =100-75=25%

Attachments

2set.JPG [ 14 KiB | Viewed 7247 times ]

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Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

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18 Aug 2013, 16:31

Tagger wrote:

The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20% B. 25% C. 40% D. 60% E. 75%

Let, total dessert ordered = T and total couple = 100 From question, 60+20% of T = T or, T = 75 % ordered dessert.

So next couple will not order dessert = 100-75 = 25 % _________________

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

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24 Jan 2014, 06:09

Let total number of couples be 100.

60% order Dessert & Coffee = 60 couples. 20% who order Dessert do not order coffee => 80% who order dessert also order coffee this is given to be 60. Hence total number of couples who order Dessert is 60*100/80 = 75. Number of couples who do NOT order Dessert = 100-75 = 25. The probability that next order will not have dessert is 25%. _________________

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

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13 Feb 2015, 00:24

Tagger wrote:

The waiter at an expensive restaurant has noticed that 60% of the couples order dessert and coffee. However, 20% of the couples who order dessert don't order coffee. What is the probability that the next couple the waiter seats will not order dessert?

A. 20% B. 25% C. 40% D. 60% E. 75%

I solved this pretty fast this way:

60% dessert and coffee --> 40% nothing, dessert, or coffee

Let them be the same probability --> 40% / 3 = 13,333%

40% - 13% = 27% --> Answer has to be around this range --> B is closest

Re: The waiter at an expensive restaurant has noticed that 60% [#permalink]

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13 Apr 2016, 05:44

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