Can't get the logic for this one

Expert replies

netneoaaa: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Wed Jun 13, 2007 3:57 am

by netneoaaa » Wed Jun 27, 2007 7:10 am

From GMAT Disclosed Edition - Test Code 31

If the average of 5 positive temperatures is x degrees farenheit, then the sum of the 3 greatest of these temperatures in degrees, farenheit could be

a) 6x
b) 4x
c) 5x/3
d)3x/2
e)3x/5

It is obviously not 6x. I tried 5x/3 which is wrong. OA is 4x. Could someone please explain why ??

Another question :

In a two way election Mr X gets 40%=942568 votes. What percent of the remaining votes would he need to have in order to have won atleast 50% of all votes cast.

a) 10
b) 12
c)15
d)17
e)20

OA is d

It is a simple question. But may be my mind is blocked. Could someone explain me the OA !!

Source: Beat The GMAT — Problem Solving | Wed Jun 27, 2007 7:10 am

harry_x1: Junior | Next Rank: 30 Posts; Posts: 26; Joined: Wed Jun 20, 2007 2:01 am

by harry_x1 » Wed Jun 27, 2007 7:24 am

let 1,2,3,4,5 be the temperatures. Their avg amounts to 3 which is x.
now sum of greatest three is 5+4+3=12.

now solve using options. only 4x=12
therefore ans=4x

drhomler: Master | Next Rank: 500 Posts; Posts: 141; Joined: Thu May 03, 2007 1:15 pm

by drhomler » Wed Jun 27, 2007 8:25 am

I concur with Harry's asessment on the first one, that is exactly how I woul dand did approach it.

For number 2:
let x =100-the number of total votes out there
60 remain becuase he recieved 40
of the orignal 100 you need 10
so you are looking for 10 out of the remaining 60 which =1/6 ot 16.67

Plugging in numbers for these types of questions usually works the best for me, and when you have percents it helps to think of 100% as 100

jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

by jayhawk2001 » Wed Jun 27, 2007 4:06 pm

For the first one, plugging in numbers would help solve the problem
quickly.

Alternatively, you can look at min / max and use POE to solve this.

For example, the min value for the sum (of 3 temp) is when all 5
values are equal i.e. x

So, sum in this case = 3x

You can immediately eliminate C, D and E as each one of them is < 3x.

You can also see that sum can't be 6x as sum of 5 temperatures = 5x.
So, discard A

Voila, B alone remains !

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