There are 16 marbles in a jar: 5 red, 3 blue, and 8 yellow. What is the probability of selecting a blue marble and then, without replacing the blue marble, selecting a yellow marble?

A. 3/32
B. 11/16
C. 173/240
D. 1/10

1 answer

To find the probability of selecting a blue marble first and then a yellow marble, we can break it down into two steps.

Step 1: Selecting a blue marble

There are 3 blue marbles out of a total of 16 marbles.

The probability of selecting a blue marble is: \[ P(\text{Blue}) = \frac{\text{Number of blue marbles}}{\text{Total number of marbles}} = \frac{3}{16} \]

Step 2: Selecting a yellow marble after removing the blue marble

After removing a blue marble from the jar, there are now 15 marbles left (because we did not replace the blue marble). The composition of the remaining marbles is:

  • 5 red marbles
  • 3 blue marbles (originally, but one has been taken out)
  • 8 yellow marbles

So the total number of yellow marbles remains 8.

The probability of selecting a yellow marble now is: \[ P(\text{Yellow | Blue}) = \frac{\text{Number of yellow marbles}}{\text{Total number of remaining marbles}} = \frac{8}{15} \]

Final Calculation: Combined Probability

Now, we multiply the probabilities of the two independent events to find the total probability of selecting a blue marble and then a yellow marble.

\[ P(\text{Blue and then Yellow}) = P(\text{Blue}) \times P(\text{Yellow | Blue}) = \frac{3}{16} \times \frac{8}{15} \]

Calculating that:

\[ P(\text{Blue and then Yellow}) = \frac{3 \times 8}{16 \times 15} = \frac{24}{240} = \frac{1}{10} \]

Thus, the probability of selecting a blue marble and then, without replacing it, selecting a yellow marble is:

\[ \boxed{\frac{1}{10}} \]