1. 7.5 Probability of Dependent Events
4/19/2013

2. Tell whether the events are independent or dependent.
You randomly select 2 cards from a standard 52-card deck.
What is the probability that the first card is not a face card and second card is a face card if you replace the first card before selecting the second card?
What is the probability that the first card is not a face card and second card is a face card if you do not replace the first card before selecting the second card.

3. Independent Events Dependent Events Definition:
2 or more events that do not have an effect on the outcomes of each event . 2 or more events where one affects the occurrence of the other.
Dependent Events
Definition:

4. Tell whether the events are independent or dependent.
You randomly select 2 cards from a standard 52-card deck.
What is the probability that the first card is not a face card and second card is a face card if you replace the first card before selecting the second card?
B. What is the probability that the first card is not a face card and second card is a face card if you do not replace the first card before selecting the second card.
Independent
Dependent

5. A bag contains 12 blue marbles and 10 yellow marbles
A bag contains 12 blue marbles and 10 yellow marbles. What is the probability that you will pull blue marble then a yellow marble?
𝑃 𝑏𝑙𝑢𝑒 = 12 22
𝑃 𝑦𝑒𝑙𝑙𝑜𝑤 = 10 21
𝑃 𝐵 𝑡ℎ𝑒𝑛 𝑌 = ∙ 10 21
= = ≈26%

6. In a deck there are 52 cards, 4 of which are aces
In a deck there are 52 cards, 4 of which are aces. What is the probability that you will pull 3 aces in a row?
4 52
3 51
2 50 = =
≈.02% ● ●
1st pull
2nd pull
3rd pull

7. Mrs. Kindred needs two students to help read an English passage in her class of 11 boys and 14 girls. If she randomly chooses one student to read, then another, what is the probability that both readers will be boys?
11 25
10 24
2nd choice
1st choice
𝑃 𝐵 𝑡ℎ𝑒𝑛 𝐵 = ∙ 10 24 = =
≈18%

8. A bag of Scrabble letters has 3 As, 1 X, 2 Bs and 5 Es left
A bag of Scrabble letters has 3 As, 1 X, 2 Bs and 5 Es left. What is the probability that you will pull an A and then an E?
3 11
5 10
1st pull
2nd pull A X
𝑃 𝐴 𝑡ℎ𝑒𝑛 𝐸 = 3 11 ∙ 5 10 B E E = A B A E E
= 3 22
≈13.6% E

9. You are on a soccer team and want to be goalkeeper in today’s game but it depends on the coach. If Scott coaches, you have a 60% chance, whereas if Andrew coaches, you have a 40% chance. However, Scott coaches 50% of the time. What is the probability that Scott will coach and youwill be goalkeeper today?

10. Homework
WS 7.5 Skip #2, 8, 10 & 14
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