BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Maths stock

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 124
Joined: Sun Mar 07, 2010 3:15 pm
Thanked: 1 times

Maths stock

by francoisph » Fri Jun 04, 2010 2:41 pm
Hi,

I disagree with kaplan s explanation

Among a group of 2500 people,
35% in invest in municipal bonds, 18% invest in oil stock
and 7% invest in both municipal bonds and oil stock
if 1 person is to be randomly selected from the 2500people
What is the probability that the person selected will be one who invests in municipal bonds but not in oil stocks??

Answer is 7/25

They took 2500 *35%=875 invest in bond
2500*7% both in bonds and oil = 175
then they sub 875 - 175 = 700 why ???
Top
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 136
Joined: Sun Sep 28, 2008 8:20 pm
Location: fssf
Thanked: 17 times

by krazy800 » Fri Jun 04, 2010 2:51 pm
francoisph wrote:Hi,

I disagree with kaplan s explanation

Among a group of 2500 people,
35% in invest in municipal bonds, 18% invest in oil stock
and 7% invest in both municipal bonds and oil stock
if 1 person is to be randomly selected from the 2500people
What is the probability that the person selected will be one who invests in municipal bonds but not in oil stocks??

Answer is 7/25

They took 2500 *35%=875 invest in bond
2500*7% both in bonds and oil = 175
then they sub 875 - 175 = 700 why ???


The question system asks the probability of selecting a person from municipal stocks alone

Municipal stocks alone = total municipal stocks (2500*35%) - ((both municipal stocks - oil bonds) (i.e. 2500*7%)

HTH!
Aiming High
Top
Senior | Next Rank: 100 Posts
Posts: 85
Joined: Sat Aug 15, 2009 4:36 am
Thanked: 19 times

by gmatjedi » Fri Jun 04, 2010 4:53 pm
2500
bonds=2500*0.35=875
oil=2500*.18=450
bonds+oil=2500*0.07=175

venn diagram

only bonds=700
bonds+oil=175
only oil=275

700/2500
=7/25
Top
Master | Next Rank: 500 Posts
Posts: 265
Joined: Mon Dec 28, 2009 9:45 pm
Thanked: 26 times
Followed by:2 members
GMAT Score:760

by mj78ind » Fri Jun 04, 2010 5:33 pm
Another approach I used:

since 35% in munis and 18% in oil and 7% common, hence only munis = 35 - 7 = 28%. We know that total 28 out of 100 people invested in munis, which means = 28/100 = 7/25. I think the 2500 number is superfluous.

Am I missing something, thanks.
Top
Senior | Next Rank: 100 Posts
Posts: 56
Joined: Fri Mar 05, 2010 9:50 pm
Thanked: 1 times

by muralithe1 » Sun Jun 06, 2010 1:13 pm
Answering 7/25 is fine when the question is "What is the probability that the person selected will be one who invests in municipal bonds "

but if the question is

"
What is the probability that the person selected will be one who invests in municipal bonds but not in oil stocks??"

Answer = probability of person selecting municipal bonds * probability of person not selecting oil stocks.
venn diagram

only bonds=700
bonds+oil=175
only oil=275

so Answer will be 700/2500 * (2500-275)/ 2500 = 623/2500

Am i crazy????
Please correct and suggest me..

Thanks,
Murali
Top
Master | Next Rank: 500 Posts
Posts: 124
Joined: Sun Mar 07, 2010 3:15 pm
Thanked: 1 times

by francoisph » Sun Jun 06, 2010 2:34 pm
ANSWER is 700/2500
=7/25
Top
Post new topic Post Reply
• Page 1 of 1