Math Is Fun Forum

NESIC

Member

Registered: 2010-09-25

Posts: 16

(Probability) Dear All kindly check solution is right

A class contains 10 men and 20 women of which half the men and half the women
have brown eyes. Find the probability that a person chosen at random is a man or has
brown eyes.

Solution:

P(Man)=10/30=.33
P(Brown)=15/30=.5
P(M intersect B)=5/30= .166
P(MUB)=P(M)+P(B)-P(M intersect B)
P(MUB)= .33 + .5 - .166
P(MUB)= .664 Ans

If solution wrong kindly guide me

Last edited by NESIC (2010-10-09 05:55:43)

soroban

Member

Registered: 2007-03-09

Posts: 452

Re: (Probability) Dear All kindly check solution is right

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bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: (Probability) Dear All kindly check solution is right

Hi NESIC;

Use your Venn diagrams while learning! Click the picture below.

P(M) = 1/3
P(B)  = 1/2

We would like to just add them up like this.

But you counted the intersected area twice (see the drawing )! So take one of them away.

The formula is easily derived from the diagram.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.