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## #1 2018-03-31 11:27:05

Hannibal lecter
Member
Registered: 2016-02-11
Posts: 222
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Five balls (2 red , 1 blue , 1 green , 1 yellow )
are arranged in a circle, Find the probability that the red balls are not together

Wisdom is a tree which grows in the heart and fruits on the tongue

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## #2 2018-03-31 20:13:35

bob bundy
Registered: 2010-06-20
Posts: 8,322

In circular type questions the first red may be anywhere as all spaces are equal.  So now consider how to place the rest.

The space to the left of the red may be any of 3.  We'll assume we use one of these. The space to the right of the red may be any from the remaining two.  Now to place the rest.  Two ways to do that.So that's three x two x two = 12 ways.
Now to consider the total number of possibilities.

We've placed one red.  Left may be one from four and right one from three and once again two ways to place the rest.  That's 24 ways.

So P = 12/24

Bob

Good luck with the exam.

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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