Download Revision Sheet for Unit 21

YEAR 9 Revision
UNIT 21: Probability
1. 140 students each study one language as shown in the table below.
French
Spanish
Female
Total
10
Male
Total
German
40
40
72
30
140
a. Complete the table.
b. If one student is picked at random, what is the probability that they study Spanish?
2. A biased die has a probability of 0.45 of landing on a 1. If you roll the die 900 times, work out
an estimate for the number of 1’s you will score.
3. A bag contains 2 red beads, 4 black beads and 3 green beads.
a. Complete the possibility space diagram to show all the possible outcomes of picking
a bead at random and replacing it, then doing the same again.
B
R
R
B
B
B
G
G
G
R, R
R, R
R,B
R, G
R, R
R, R
B, B
B, R
B, R
B, R
B, R
B, B
G, R
G, R
G, R
G, R
G, B
b. How many possible outcomes of the experiment are there?
c. Use your table to calculate the probability that both beads are the different colours.
A young baby can be on happy, crying or asleep. The probability that the baby is happy is
0.12, the probability that it is asleep is 0.58. What is the probability that it is crying?
Melissa says that the probability that she is naughty for mummy tonight is 0. She is wrong.
Explain why.
Dan and James take a test. The probability that Dan passes is 0.85 and the probability that
James passes is 0.7.
a. Complete a tree diagram.
b. Calculate the probability that only one of them passes the test.
Fred experiments. He tosses a coin 50 times. He gets tails 35 times. Is the coin fair? Explain
your answer.
The probability that Callum is late for school tomorrow is 0.2 and the probability that Martin
is late for school is 0.4. The two events are independent.
a. What is the probability that both boys are late?
b. What is the probability that neither boy is late?
(3 marks)
R
R
B
B
B
B
G
G
G
4.
5.
6.
7.
8.