probability Q-1

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speed: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Wed Aug 22, 2007 9:41 pm

by speed » Mon Aug 27, 2007 8:54 pm

help me to solve these probability questions

1.In a bag of balloons, the ratio of red balloons to other colours is 1:5, if 3 balloons are selected from the bag at random, what is the probability that (a) at least one balloon is red, (b) exactly one balloon is red.?

speed

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Source: Beat The GMAT — Problem Solving | Mon Aug 27, 2007 8:54 pm

ratindasgupta: Senior | Next Rank: 100 Posts; Posts: 98; Joined: Mon Jun 11, 2007 10:32 pm; Location: Mumbai

by ratindasgupta » Mon Aug 27, 2007 10:53 pm

Assume that 1 balloon is red and there are 5 balloons of other colours.

Atleast 1 red = 1 - (no red)

No red = 5/6 x 4/5 x 3/4 = 1/2

Atleast 1 red = 1- 1/2 = 1/2

Exactly 1 red = (1C1 x 5C2)/6C3 = 1/2

Whats the OA?

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