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Q.

A box contains 54 marbles each of which is blue, green or white. The probability of selecting a blue marble at random from the box is 13 and the probability of selecting a green marble at random is 49.  What is the number of white marbles in the box?


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a

54

b

12

c

18

d

24 

answer is B.

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Detailed Solution

Given, a box contains 54 marbles each of which is blue, green or white. The probability of selecting a blue marble at random from the box is 13 and the probability of selecting a green marble at random is 49. We know that,
   Probability of an event =  Number of favourable outcomes   Total number of outcomes   
The total number of outcomes is given as 54.
Let the number of favourable outcomes for getting a blue marble be b.
Now, the probability of finding the blue marble is b 54   Therefore, 1 3 = b 54   b is 18.
Let the number of favourable outcomes for getting a green marble be g
The probability of finding the green marble is 4 9  
g 54 = 4 9   g is 24.
Let the number of favourable outcomes for getting a white marble be w.
Now, we can say that,
18+24+w=54 w=12   So, the total number of marbles in the jar is 12 white marbles.
Hence, the correct option is 2.
 
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