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Gmat club PS.

by bblast » Sat Jul 02, 2011 9:30 am
I could solve this by venn diagram, a matrix approach solution would be much appreciated to find the no of people knowing c++ as well as VB.

If among 200 programmers working for an IT company, 30% know C++, 80% know Visual Basic, and 10% do not know either of these computer languages, in how many ways can a team of three programmers, all knowing both C++ and Visual Basic, be formed?

2960
3990
6840
8820
9880


OA- 40C3


-------c++-----c+not-----total
VB------X------_____-----160
vbnot---__------ 20 -----___
total---60-----_____-----200


kindly fill in the blanks above to find the value of X.
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by Frankenstein » Sat Jul 02, 2011 9:44 am
Hi,
-------c++-----c+not-----total
VB------ 40(3)----_____-----160
vbnot---20(2)__------ 20 -----40(1)__
total---60-----_____-----200

The number in the bracket indicates the order of calculation.
In the last column 160 and 200 are there. the missing blank will be 40.From this we calculate c++andVbnot in 2nd row and then BC and C++ from 1st column.
So, number of groups formed is 40C3.
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by ntamhane » Sat Jul 02, 2011 10:07 am
A good approach would be a venn diagram, My approach to solve this problem is:
30% of 200 = 60 know c++
80% of 200 = 160 know VB
10% of 200 = 20 know nothing
so 160+60+20 = 240.
240-200 = 40 who know both
3 programmers to be chosen from 40 i.e. 40C3 = 9880
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by bblast » Sat Jul 02, 2011 11:00 am
@ntamhane- Agree that the venn diagram for this question was cheese, and matrix is complicated here, but we should scrutinize and solve each problem is all possible ways for better understanding.

Frank- I did not get how did u work out the values in the first column ? can u rephrase things pls.
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by Frankenstein » Sat Jul 02, 2011 11:08 am
Hi,
-------c++-----c+not-----total
VB------X------_____-----160
vbnot---__------ 20 -----___
total---60-----_____-----200
Step-1:
-------c++-----c+not-----total
VB------X------_____-----160
vbnot---__------ 20 -----_40__
total---60-----_____-----200
Column3 --> 160+ _ =200.

Step-2:
-------c++-----c+not-----total
VB------X------_____-----160
vbnot--_20_------ 20 -----_40__ --> _+20 = 40. So missing value is 20
total---60-----_____-----200

Step-3:
-------c++-----c+not-----total
VB------X------_____-----160
vbnot--_20_------ 20 -----_40__ -
total---60-----_____-----200
Column1 --> x+20 = 60. So, x = 40
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by bblast » Sun Jul 03, 2011 12:39 am
Shahhh!!!!I missed that - ended up getting this wrong in timed mode, was pressed for time, this was pretty straight forward- and then my clogged brains wont work after 12 am in the night. :oops:

thanks Frank- i hope ur new signature is not inspired from "Prestige" ?
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by Frankenstein » Sun Jul 03, 2011 10:48 am
bblast wrote: thanks Frank- i hope ur new signature is not inspired from "Prestige" ?
Off topic:
No. It is not from 'The Prestige'.
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by amit2k9 » Sun Jul 03, 2011 10:56 pm
its comes to 20% of 200 = 40 people.

thus 40c3.

----v--- v!
C--20---- 10--- 30

C!-60-----10----70

---80-----20----100
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