Grade 7 · Math · Unit 14 of 20
Dependent Events
With and without replacement
What your child practises
Telling independent from dependent events and finding the probability of two events, with and without putting the first item back.
Ontario Curriculum expectation: D2.1, D2.2 · independent and dependent events, and probabilities of two events
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A café has 3 kinds of sandwich and 3 kinds of drink. How many different sandwich-and-drink combinations are possible?
- 15
- 9
- 14
Show answer
9
Hint: Multiply the number of choices.
Question 2
A bag has 5 red and 5 blue marbles. You take two marbles without putting the first one back. What is the probability that both are red?
- 2/9
- 1/2
- 1/4
Show answer
2/9
Hint: Multiply the probability of the first red by the probability of the second red, after the first is gone.
Question 3
A bag has 3 red and 5 blue marbles. You take out one marble, put it back, then take out another. What is the probability that both are red?
- 3/8
- 9/64
- 3/28
Show answer
9/64
Hint: The first pick is put back, so the second pick has the same chances as the first. Multiply them.
Question 4
A bag has 5 red and 1 blue marbles. You take out a red marble and do not put it back. What is the probability that the second marble is red?
- 4/5
- 1
- 5/6
Show answer
4/5
Hint: After the first pick, there is one fewer red marble and one fewer marble in all.
Question 5
A bag has 2 red and 1 blue marbles. You take two marbles without putting the first one back. What is the probability that both are red?
- 1/3
- 4/9
- 2/3
Show answer
1/3
Hint: Multiply the probability of the first red by the probability of the second red, after the first is gone.
Question 6
You draw a card, keep it out, then draw again. Are the two draws independent or dependent?
- independent
- dependent
Show answer
dependent
Hint: Independent: the first event does not change the second. Dependent: it does.