Question

A jar contains 54 marbles each of which is blue, green or white. The probability of selecting a blue marble at random from the jar is 1/3, and the probability of selecting a green marble at random is 4/9. How many white marbles does the jar contain? 

(A) 12 

(B) 6 

(C) 9

(D) 11

Answer 1

The correct option is: (A) 12 

Explanation:

Let there be b blue, g green and w white marbles in the jar. Then, b + g + w = 54                ....(i)

. ^.. P (Selecting a blue marble) = b/54

It is given that the probability of selecting a blue marble is 1/3.

. ^.. 1/3 = b/54 => b = 18

We have, P (Selecting a green marble) = 4/9 (given)

=> g/54 = 4/9 => g = 24

Substituting the values of b and g in (i), we get 

18 + 24 + w = 54 + w = 12 

Hence, the jar contains 12 white marbles.