# 11.4.1. Calculating Probability

Two cards are drawn one after the other from a set of 6 identical cards numbered from 1 to 6. Given that the drawn card must be returned before another card is drawn, determine the event in which the sum of the two numbers is less than 5.

- A
- B
- C
- D

### Example

Two cards are drawn one after the other from a set of 6 identical cards numbered from 1 to 6. Given that the drawn card must be returned before another card is drawn, determine the event in which the sum of the two numbers is less than 5.

### Solution

Since the event is selecting two cards, where the sum of the two cards drawn is less than 5, the sum of the two cards must be 2, 3, or 4. To get a sum of 2, the two cards must be 1 and 1. To get a
sum of 3, the two cards can either be 1 and 2 or 2 and 1. To get a sum of 4, the two cards can be 1 and 3, 2 and 2, or 3 and 1. Thus, the set