kaplan rate quetion

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resilient: Legendary Member; Posts: 789; Joined: Sun May 06, 2007 1:25 amFollowed by: 6 members; Location: Southern California, USA; Thanked: 15 times

by resilient » Tue Mar 18, 2008 9:29 am

in 1966, the operative mortality rate in open heart surgery at certain hospital was 8.1 per 100 cases. By 1974, the operative mortality rate had declined to 4.8 per 100 cases. If the rate declined by 20 % from 1973- 19474, by approximately what perent did it decline from 1966 to 1973?

a. 6%
b.21%
c.26%
d.41%
e.49%

Stuart can you help, this is a pretty easy question but I am getting lost in the words and not understanding the question and how to move forward!

qa is C..

Appetite for 700 and I scraped my plate!

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Source: Beat The GMAT — Problem Solving | Tue Mar 18, 2008 9:29 am

xilef: Master | Next Rank: 500 Posts; Posts: 111; Joined: Thu Jan 31, 2008 4:05 pmFollowed by: 1 member; Thanked: 18 times

by xilef » Tue Mar 18, 2008 9:58 am

We need to find the rate reduction from 1966 to 1973. We have 1966 but not 1973. We know that the rate for 1974 is 4.8 which is a 20% reduction from 1973. Let the rate for 1973 be X:

X-(.2X)=4.8
X= 4.8/.8
X=6

Now we know that the rate in 1973 was 6 per 100 cases, so the reduction from 1966 to 1973 is 8.1-6 or 2.1. The questions asks for %, so we find that 2.1 is 26% of 8.1. Answer C.

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resilient: Legendary Member; Posts: 789; Joined: Sun May 06, 2007 1:25 amFollowed by: 6 members; Location: Southern California, USA; Thanked: 15 times

xilef

by resilient » Wed Mar 19, 2008 8:14 am

For some reason, I am trying to answer this in a much different way. I cant see the logic in the way you set up your equation.

my way: I wanted to get 80% of the difference between 8.1 and 4.8 and this will get my number for 1973. After that the rest is easy! Am I on the right track?

Appetite for 700 and I scraped my plate!

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xilef: Master | Next Rank: 500 Posts; Posts: 111; Joined: Thu Jan 31, 2008 4:05 pmFollowed by: 1 member; Thanked: 18 times

by xilef » Wed Mar 19, 2008 10:27 am

4.8 in 1974 is 80% of the rate in 1973, that's what 20% reduction means. Now you know both 1966 and 1973, from here you can find the rate reduction %.

No, you can't take 80% of the difference between 8.1 and 4.8.
4.8 is 80% of 6 and you are looking for what % is 2.1 (8.1-6) of 8.1.
You should review percentages.

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resilient: Legendary Member; Posts: 789; Joined: Sun May 06, 2007 1:25 amFollowed by: 6 members; Location: Southern California, USA; Thanked: 15 times

i understand

by resilient » Thu Mar 20, 2008 9:07 am

I have a pretty good handle on the percentages. I see where I went wrong. I misunderstood the last sentence. I overall looked at the question in the wrong way! Thanks Xilef!

Appetite for 700 and I scraped my plate!

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