Question

The probability of selecting a blue marble at random from a jar that contains only black blue and green marbles is 1/5 the probability of selecting a black marble at random from the same jar is 1/4. If the jar contains 11 green marbles, find the total number of marbles in the jar.

Answer 1

Answer:

20 marbles.

Step-by-step explanation:

Point to note :

Total Probability = sum of all probabilities and is always equal to 1.

P(selecting a blue marble) = 1/5

P(selecting a black marble) = 1/4

P(selecting a green marble) = 1 - (1/4 + 1/5)

1/5 + 1/4 = 9/20

20/20 - 9/20 = 11/20

This is the probability of getting a green marble.

There 11 green marbles and hence :

11/20 = 11

The total number of marbles is :

20/11 × 11 = 20

20 marbles

Answer 2

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