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At a certain hospital, 75% of the interns receive fewer than [#permalink]
25 Dec 2007, 21:01

1

This post was BOOKMARKED

At a certain hospital, 75% of the interns receive fewer than 6 hours of sleep and report feeling tired during their shifts. At the same time, 70% of the interns who receive 6 or more hours of sleep report no feelings of tiredness. If 80% of the interns receive fewer than 6 hours of sleep, what percent of the interns report no feelings of tiredness during their shifts?

A, 6
B, 14
C, 19
D, 20
E, 81

Please explain in detail with your answer. I don't know if I can answer this question in 2 to 4 minutes. Is there is a quicker way to get to the answer. I tried the double-matrix table option.

Re: overlapping sets [#permalink]
27 Jan 2008, 08:21

im not sure what im doing wrong here, but the answer i get isnt one of the choices :-S

I assumed 100 total interns. 80% overall gets less than 6 hrs sleep, so thats 80 people. Of the 80, 75% feel tired ... thats 60 people who are tired, and 20 who arent.

Then we have 20 people who get more than 6 hours of sleep, but 70% of them, i.e. 14 people arent tired ... that leaves 6 people who are tired.

The total # of people who arent tired are the 20 people + 14 people = 34 people, which should be 34% ....

Re: overlapping sets [#permalink]
27 Jan 2008, 08:57

pinal2 wrote:

At a certain hospital, 75% of the interns receive fewer than 6 hours of sleep and report feeling tired during their shifts. At the same time, 70% of the interns who receive 6 or more hours of sleep report no feelings of tiredness. If 80% of the interns receive fewer than 6 hours of sleep, what percent of the interns report no feelings of tiredness during their shifts?

A, 6 B, 14 C, 19 D, 20 E, 81

Please explain in detail with your answer. I don't know if I can answer this question in 2 to 4 minutes. Is there is a quicker way to get to the answer. I tried the double-matrix table option.

thanks

Let's make this super easy guys. We'll say we have 200 interns.

200 interns 150 (75%) get fewer than 6 hours of sleep and report feeling tired 160 (80%) get fewer than 6 hours of sleep 40 (200-160) get more than 6 hours of sleep 28 (70% of 40) get more than 6 hours of sleep and don't report feeling tired

(160-150)+28 = 38 interns don't report feeling tired. (160-150 comes from 160 getting fewer than 6 hours of sleep, but only 150 of that number saying they feel tired. meaning 10 don't feel tired) 38/200 = 19%

Re: overlapping sets [#permalink]
27 Jan 2008, 09:00

Quote:

I assumed 100 total interns. 80% overall gets less than 6 hrs sleep, so thats 80 people. Of the 80, 75% feel tired ... thats 60 people who are tired, and 20 who arent.

The question is saying 75% of the TOTAL receive fewer than 6 hours of sleep and report feeling tired. Then it says 80% get fewer than 6 hours of sleep, so 80-75 = 5% don't feel tired and get less than 6 hours of sleep.

Then you did the other part correctly and got 14% so 14+5 = 19%

Re: overlapping sets [#permalink]
27 Jan 2008, 17:17

You use a table to solve this. You want to pay attention to what you are taking percentages of, either the total or another number. If percent questions like this, that do not give a total, just pick a number. I picked 100. --------------------Less 6 hours----More 6 hours--------------Total Report Tired---------75%(100)---------blank------------------blank

No Report------------5----------------70%(x)-----------------Solve for

Re: overlapping sets [#permalink]
27 Jan 2008, 18:22

pinal2 wrote:

At a certain hospital, 75% of the interns receive fewer than 6 hours of sleep and report feeling tired during their shifts. At the same time, 70% of the interns who receive 6 or more hours of sleep report no feelings of tiredness. If 80% of the interns receive fewer than 6 hours of sleep, what percent of the interns report no feelings of tiredness during their shifts?

A, 6 B, 14 C, 19 D, 20 E, 81

Please explain in detail with your answer. I don't know if I can answer this question in 2 to 4 minutes. Is there is a quicker way to get to the answer. I tried the double-matrix table option.

thanks

total number of interns = 100

Sleeping < 6 hrs = 75 ( all tired )

Therefore sleeing > 6 hrs = (100-75) = 25

Not tired = 70% of 25

Condition If Sleeping < 6 hrs = 80 ( all tired )

Therefore sleeing > 6 hrs = (100-80) = 20

Not tired = 70% of 20 = "14"

Further you know......

gmatclubot

Re: overlapping sets
[#permalink]
27 Jan 2008, 18:22