Question

3. A bag has five blue marbles, seven red marbles and nine green marbles. Three marbles are drawn

without replacement. Determine the probability of drawing a green marble, then a blue marble,
and then another green marble. [7 marks/K]

Answer 1

The probability is 9/266

Explanation:

The first thing to do here is get the total number of marbles = 5 + 7 + 9 = 21 marbles

Now we are drawing the marbles without replacement, this means once a marble is drawn there is a decrease in the total number of marbles left.

The probability of drawing a green marble initially = number of green marbles/ total

number of marbles = 9/21 = 3/7

Now, we want to draw a blue marble

There are 5 blue marbles and we have already drawn one marble from the total. So the probability of drawing a blue marble would be 5/20 = 1/4

And lastly, another green marble

That would make 6 green marbles left and a total of just 19 left. So the probability at this point for green marbles = 6/19

Having and in probability means we multiply all

So this means the probability we are calculating is; 3/7 * 1/4 * 6/19 = 18/(28 * 19) = 9/(14 * 19) = 9/266