Question

Suppose a jar contains 9 red marbles and 13 blue marbles. If you reach in the jar and pull out 2 marbles at random, find the probability that both are red. Write your answer in decimal form, rounded to the nearest thousandth.

Answer 1

Answer: P = 0.156

Step-by-step explanation:

Initially in the jar, we have 9 red and 13 blue marbles, so we have a total of 22 marbles in the jar.

If we want to take a red ball for the jar, the probability of getting one is equal to the number of red balls divided by the total number of balls, so:

P1 = 9/22 .

Now, suppose you already took one red ball, we want to take the second one; the probability is calculated in the same way, but now we already took a red ball, so we have 8 red balls and 21 balls in total; so:

P2 = 8/21

Now the probability of both events to happen is equal to the product of their probabilities:

P = P1*P2 = (9/22)*(8/21) = 0.1558

Now we want to round it to the nearest thousandth.

The thousandth is the second number after the decimal point, and the number that comes after is an 8, so we need to round it up; then we get:

P = 0.156, or 15.6% in percentage form.