# 11.4.1. Calculating Probability

John wrote 20 letters and found out that of them have no mistakes, and Dina wrote 28 letters and found out that of them also don’t have any mistakes. If a letter is selected randomly from all the written letters, determine the probability of the letter having mistakes and being written by John.

• A
• B
• C
• D

### Example

John wrote 20 letters and found out that of them have no mistakes, and Dina wrote 28 letters and found out that of them also don’t have any mistakes. If a letter is selected randomly from all the written letters, determine the probability of the letter having mistakes and being written by John.

### 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 selecting a letter with mistakes that has been written by John. Find the probability of event as follows:

Thus, the probability of selecting a letter with mistakes that has been written by John is

0
correct
0
incorrect
0
skipped