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A box contains 2 white and 3 blue identicalMarbles. If two marbles are picked at...


Question

A box contains 2 white and 3 blue identical

Marbles. If two marbles are picked at random,

One after the other without replacement, what is

The probability of picking two marbles of different

Colours?

Options

A) 2/3

B) 3/5

C) 2/5

D) 7/20

E) 3/10

The correct answer is B.

Explanation:

Total number of marbles = 5; 1st pick = 2/5 2nd pick = 3/4; 3rd pick = 3/5; 4th pick = 2/4
∴ Probability of picking two marbles of different colours = (2/5 x 3/4) + (3/5 + 2/4) = 12/20 = 3/5

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Dicussion (1)

  • Total number of marbles = 5; 1st pick = 2/5 2nd pick = 3/4; 3rd pick = 3/5; 4th pick = 2/4
    ∴ Probability of picking two marbles of different colours = (2/5 x 3/4) + (3/5 + 2/4) = 12/20 = 3/5

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