probablity

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[email protected]: Senior | Next Rank: 100 Posts; Posts: 30; Joined: Sun Jun 27, 2010 7:55 pm

by [email protected] » Wed Jun 30, 2010 9:11 pm

A group of 50 students were required to clear 2 tasks, one in rock-climbing and the other in bridge crossing during an adventure sports expedition. 30 students cleared both the tasks. 37 cleared bridge crossing, 38 students cleared rockclimbing. How many students could not clear any task?

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Source: Beat The GMAT — Problem Solving | Wed Jun 30, 2010 9:11 pm

gmatmachoman: Legendary Member; Posts: 2326; Joined: Mon Jul 28, 2008 3:54 amFollowed by: 2 members; Thanked: 173 times; GMAT Score:710

by gmatmachoman » Wed Jun 30, 2010 9:24 pm

[email protected] wrote:A group of 50 students were required to clear 2 tasks, one in rock-climbing and the other in bridge crossing during an adventure sports expedition. 30 students cleared both the tasks. 37 cleared bridge crossing, 38 students cleared rockclimbing. How many students could not clear any task?

P(AUB)= P(A) +P(B) -P(AnB)

= 37+38-30
=45

Total= P(AUB) + Neither of the both

50 = 45+X

X=5

R&D on GMAT algorithm:

https://www.beatthegmat.com/r-d-on-gmat- ... tml#305739

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selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Wed Jun 30, 2010 9:25 pm

Total=50

P(RnB)=30

P(R)=38

P(B)=37

Total=P(R)+P(B)-P(RnB)+neither

50=38+37-30+neither

neither = 5

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