Step 1: Find the possible out comes of an event

NOTE: Saying that a marble is drawn at random means all the marbles are equally likely to be drawn.

Therefore, the number of possible outcomes = 5 + 8 + 4 = 17

Let R denote the event 'marble is red

W denote the event 'the marble is white',

G denote the event 'the marble is green'

Step 2: Determine the number of outcomes favourable to the event

(i) Number of red marbles = 5

The number of outcomes favourable to the R = 5

(ii) Number of white marbles = 8

The number of outcomes favourable to the W = 8

(ii) Number of green marbles = 4

The number of outcomes favourable to the G = 4

Step 3: Calculate the probability

The probability to draw red marble P(R)= \frac{\text{ favourable outcomes}}{\text{Total possible outcomes}} = \frac{5}{17}

Similarly,

The probability to draw white marble P(W) = \frac{8}{17}

The probability to draw green marble P(G) = \frac{4}{17}

Note that P(W) + P(G) + P(R) = 1.