Unit 3
4 marks · Normal(a) The probability of picking a red bead from bag A is 0.4. The probability of picking a red bead from bag B is 0.6. Each bag contains only red and blue beads. A bead is picked from each bag. What is the probability both beads are red?
(b) If the mean of four numbers is 12.5, what is their total?
(c) Write down all the factors of 30.
Probability both beads are red.
If the mean of four numbers is 12.5, what is their total?
List all the factors of 30.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 0.24 · must show 0.24
(b) 50 · must show 50
(c) 1, 2, 3, 5, 6, 10, 15, 30 · must show 1, 2, 3, 5, 6, 10, 15, 30
Common mistakes: Multiplying probabilities incorrectly; Not listing 1 and 30 in factors
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Multiplies probabilities for independent events (0.4×0.6).
A1 (b) · 1 mark · Mean × number = total, 12.5×4=50.
M2 (c) · 1 mark · Identifies all factors of 30, attempts listing.
A2 (c) · 1 mark · Lists all factors: 1, 2, 3, 5, 6, 10, 15, 30.
Worked solution
(a) 0.4 × 0.6 = 0.24.
(b) 12.5 × 4 = 50.
(c) Factors: 1, 2, 3, 5, 6, 10, 15, 30.