Interns at hospital -MGMAT test Question

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iikarthik: Senior | Next Rank: 100 Posts; Posts: 57; Joined: Sun Jul 06, 2008 10:52 am; Thanked: 1 times; GMAT Score:640

Interns at hospital -MGMAT test Question

by iikarthik » Wed Jul 21, 2010 10:15 am

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?
6
14
19
20
81

Hi,
This is a MGMAT test Question.

Though the solution was given using some matrix method,i didnt get that.
can someone pls explain?

OA = 19

Thanks
karthik

Quote

Source: Beat The GMAT — Problem Solving | Wed Jul 21, 2010 10:15 am

ptandon: Senior | Next Rank: 100 Posts; Posts: 36; Joined: Thu Jan 03, 2008 1:54 pm; Location: Arizona

by ptandon » Wed Jul 21, 2010 12:23 pm

I got this question wrong when I first attempted it 3 weeks ago in the Practice Test. Never really tried to solve it at that time, since I decided to go through the concepts first.
I gave it a shot just now, and nailed it. Here's what I did:
Given: 75% interns who receive fewer than 8 hrs of sleep report feeling of tiredness.
Means: If 80% of interns receive fewer than 8 hrs of sleep, then only 5% do NOT report feeling of tiredness.

Given: 70% of interns who receive more than 8 hrs of sleep report feeling of tiredness.
Means: 14% of TOTAL interns do NOT feel tired, while 6% report feeling of tiredness.

Adding above the 5% and 14%, you get 19%.

You could also take the 75% (given fact) and add the 6% (calculated above), which gives you a total of 81% that feel tired.
Then calculate the % NOT tired as 100% - 81% = 19%.

Hope this helps.

Quote

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pm; Location: New York, NY; Thanked: 13060 times; Followed by:1906 members; GMAT Score:790

by GMATGuruNY » Wed Jul 21, 2010 6:39 pm

iikarthik 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?
6
14
19
20
81

Hi,
This is a MGMAT test Question.

Though the solution was given using some matrix method,i didnt get that.
can someone pls explain?

OA = 19

Thanks
karthik

In this problem we have two groups (those who got less than 6 hours sleep and those who got 6 hours or more) being further divided into smaller groups (those who were tired and those who were not).

When a problem discusses groups being further divided into smaller groups, use the group grid to organize the information.

The attached .pdf gives step by step instructions for filling out the grid. The idea is that all the numbers in the grid have to add up horizontally and vertically.

Hope this helps!

Attachments

BTG_group_grid.pdf: (70.35 KiB) Downloaded 164 times

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