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probability

by hakyology » Sun Jul 06, 2008 11:50 am

There is a totla of 120 marbles in a box, each of which is red, green, blue or white. If one of marble is drawn from the box at random, the probability that it will be white is 1/4 and the probability that it will be green is 1/3. What is the probability that the marble will be either red or blue?

A) 1/6
B) 1/4
C) 2/7
D) 1/3
E) 5/12

Please explain. Thanks.


The answer is E.
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by sibbineni » Sun Jul 06, 2008 11:54 am
Given Data:
Total no of marbles:120
The probability of white is 1/4==>30 White
The probability of green is 1/3==>40 Green
so the rest will be either red or blue

120-30-40==>50 red or blue

so the probability of red or blue is 50/120===>5/12
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by andes1 » Sun Jul 06, 2008 1:59 pm
The easy way
RED GREEN WHITE BLUE
?------1/3--------1/4------?

OK. NOW MAKE A SUM
1/3 + 1/4 …. = 7/12
This is the combined probability of green and white.

Now only make a sustracction from the 100% or total that is 12/12, or simply 1

1- 7/12 = 5/12
That is the probability of blue and red combined.
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