# 11.4.1. Calculating Probability

A box contains 11 white balls, red ones, and black ones. If a ball is drawn randomly from it, where the probability that the ball is white , and the probability that the ball is red , then the number of the red balls , and the number of the black balls .

• A6, 3
• B11, 6
• C11, 3
• D3, 6

### Example

A box contains 11 white balls, red ones, and black ones. If a ball is drawn randomly from it, where the probability that the ball is white , and the probability that the ball is red , then the number of the red balls , and the number of the black balls .

### Solution

The probability of event occurring is equal to the number of favorable outcomes divided by the total number of possible outcomes in the sample space, . In this case, event is drawing a white ball. Find the total number of possible outcomes in the sample space, or the total number of balls in the box, as follows:

The probability of event occurring is equal to the number of favorable outcomes divided by the total number of possible outcomes in the sample space, . In this case, event is drawing a red ball. Now find the number of favorable outcomes for event , or the number of red balls in the box.

This means that there are 6 red balls in the box, so there must be black balls in the box.

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