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O Level Elementary Mathematics Statistics Probability Quiz

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O Level Elementary Mathematics From Real Exams Generated by Qwen3.6 Plus Updated 2026-08-17

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Questions

O-Level Elementary Mathematics Quiz - Statistics Probability

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 45

Duration: 50 Minutes
Total Marks: 45

Instructions:

Answer all questions.
Write your answers in the spaces provided.
Show all necessary working clearly; no marks will be given for correct answers without working.
Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place for angles in degrees, unless otherwise specified.
The use of an approved calculator is expected where appropriate.

Section A: Data Handling and Analysis (20 Marks)

1. The heights, $h$ cm, of 30 students in a class are recorded in the following stem-and-leaf diagram.

Stem | Leaf
  15 | 2 4 5 8
  16 | 0 1 1 3 5 5 7 8 9
  17 | 0 2 2 4 5 6 8 9
  18 | 1 3 5

Key: $15 | 2$ represents 152 cm.

(a) Find the median height.
................................................................................................................................................... [1]

(b) Find the interquartile range of the heights.
................................................................................................................................................... [2]

2. A survey was conducted on the number of hours spent on homework by 50 students. The results are summarised in the cumulative frequency table below.

Time ( $t$ hours)	$0 < t \le 1$	$1 < t \le 2$	$2 < t \le 3$	$3 < t \le 4$	$4 < t \le 5$
Cumulative Frequency	5	18	35	46	50

(a) Draw a cumulative frequency curve for this data on the grid provided below.
[Grid axes: x-axis 0 to 5, y-axis 0 to 50]

[3]

(b) Use your graph to estimate the number of students who spent more than 3.5 hours on homework.
................................................................................................................................................... [2]

3. The mean mass of 8 boys is 65 kg. The mean mass of 12 girls is 55 kg.
Calculate the mean mass of the 20 students.

...................................................................................................................................................
...................................................................................................................................................
................................................................................................................................................... [2]

4. The table shows the distribution of marks obtained by 40 students in a Mathematics test.

Mark ( $x$ )	1	2	3	4	5
Frequency ( $f$ )	4	8	12	10	6

(a) Calculate the mean mark.
................................................................................................................................................... [2]

(b) Calculate the standard deviation of the marks.
...................................................................................................................................................
...................................................................................................................................................
................................................................................................................................................... [3]

5. Two box-and-whisker plots represent the scores of Class A and Class B in a Science quiz.

Class A: Min=10, Q1=25, Median=40, Q3=55, Max=70
Class B: Min=20, Q1=35, Median=45, Q3=50, Max=65

(a) Which class has the larger interquartile range? Show your working.
................................................................................................................................................... [1]

(b) A student argues that Class B performed better because it has a higher median. Give one reason, based on the spread of the data, why Class A might be considered more consistent or inconsistent compared to Class B.
................................................................................................................................................... [1]

Section B: Probability Basics (15 Marks)

6. A bag contains 5 red balls, 3 blue balls, and 2 green balls. A ball is chosen at random.
Find the probability that the ball is:

(a) Red
................................................................................................................................................... [1]

(b) Not Blue
................................................................................................................................................... [1]

7. A fair six-sided die is thrown once.
Find the probability of obtaining:

(a) A prime number
................................................................................................................................................... [1]

(b) A number greater than 4
................................................................................................................................................... [1]

8. The probability that it rains on any given day in April is 0.3.
Calculate the probability that it does not rain on a specific day in April.

................................................................................................................................................... [1]

9. Events $A$ and $B$ are mutually exclusive. $P(A) = 0.4$ and $P(B) = 0.25$ .
Find $P(A \cup B)$ .

................................................................................................................................................... [1]

10. A spinner has 4 equal sections labelled 1, 2, 3, and 4. The spinner is spun twice.
Draw a possibility diagram to show all possible outcomes.

[2]

11. Using the possibility diagram from Question 10, find the probability that the sum of the two scores is:

(a) Exactly 5
................................................................................................................................................... [1]

(b) Less than 4
................................................................................................................................................... [1]

12. Two fair coins are tossed.
List the sample space and find the probability of getting exactly one Head.

13. In a group of 100 students, 60 study Physics, 50 study Chemistry, and 20 study both.
A student is chosen at random. Find the probability that the student studies:

(a) Neither Physics nor Chemistry
................................................................................................................................................... [2]

(b) Physics only
................................................................................................................................................... [1]

Section C: Combined Events and Applications (10 Marks)

14. A bag contains 4 white balls and 6 black balls. Two balls are drawn from the bag without replacement.
Find the probability that:

(a) Both balls are white.
...................................................................................................................................................
................................................................................................................................................... [2]

(b) One ball is white and the other is black.
...................................................................................................................................................
................................................................................................................................................... [2]

15. The probability that John passes his Mathematics exam is 0.8. The probability that he passes his Science exam is 0.7. The events are independent.
Find the probability that John:

(a) Passes both exams.
................................................................................................................................................... [1]

(b) Passes exactly one of the exams.
...................................................................................................................................................
................................................................................................................................................... [2]

16. A box contains tickets numbered 1 to 20. One ticket is drawn at random.
Let $A$ be the event that the number is a multiple of 3.
Let $B$ be the event that the number is even.

(a) Find $P(A)$ .
................................................................................................................................................... [1]

(b) Find $P(A \cap B)$ .
................................................................................................................................................... [1]

(c) Find $P(A \cup B)$ .
................................................................................................................................................... [1]

17. A bag contains 3 red marbles and 7 blue marbles. Two marbles are drawn with replacement.
Find the probability that:

(a) Both marbles are red.
................................................................................................................................................... [1]

(b) The first marble is red and the second is blue.
................................................................................................................................................... [1]

18. The table below shows the number of cars sold by a dealership over 50 days.

Number of Cars	0	1	2	3	4
Frequency	5	15	20	8	2

Calculate the mean number of cars sold per day.

19. The heights of plants in a garden are normally distributed with a mean of 30 cm and a standard deviation of 5 cm.
A plant is selected at random.

(a) State the probability that the plant's height is within one standard deviation of the mean.
................................................................................................................................................... [1]

(b) Calculate the height that is exactly two standard deviations above the mean.
................................................................................................................................................... [1]

20. A committee of 3 people is to be chosen from a group of 5 men and 5 women.
Find the total number of different committees that can be formed if there are no restrictions on gender.

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Answers

O-Level Elementary Mathematics Quiz - Statistics Probability (Answer Key)

1.
(a) Median:
Total $n = 30$ . Median position is $\frac{30+1}{2} = 15.5$ th value.
15th value = 169, 16th value = 170.
Median = $\frac{169 + 170}{2} = 169.5$ cm.
[1]

(b) Interquartile Range (IQR):
$Q_1$ position = $\frac{30+1}{4} = 7.75$ th value $\approx$ 8th value = 165.
$Q_3$ position = $\frac{3(30+1)}{4} = 23.25$ th value $\approx$ 23rd value = 176.
$IQR = Q_3 - Q_1 = 176 - 165 = 11$ cm.
[2]

2.
(a) Cumulative Frequency Curve:
Points plotted: $(1, 5), (2, 18), (3, 35), (4, 46), (5, 50)$ .
Smooth curve drawn through points, starting from $(0,0)$ .
[3]

(b) Estimation:
At $t = 3.5$ , read from graph.
Cumulative frequency $\approx 40.5$ (Accept 40–41).
Students spending more than 3.5 hours = $50 - 40.5 = 9.5$ .
Answer: 9 or 10 students.
[2]

3.
Total mass of boys = $8 \times 65 = 520$ kg.
Total mass of girls = $12 \times 55 = 660$ kg.
Total mass = $520 + 660 = 1180$ kg.
Total students = $8 + 12 = 20$ .
Mean mass = $\frac{1180}{20} = 59$ kg.
[2]

4.
(a) Mean:
$\sum fx = (1\times4) + (2\times8) + (3\times12) + (4\times10) + (5\times6) = 4 + 16 + 36 + 40 + 30 = 126$ .
$\sum f = 40$ .
Mean = $\frac{126}{40} = 3.15$ .
[2]

(b) Standard Deviation:
$\sum fx^2 = (1^2\times4) + (2^2\times8) + (3^2\times12) + (4^2\times10) + (5^2\times6) = 4 + 32 + 108 + 160 + 150 = 454$ .
Variance = $\frac{\sum fx^2}{\sum f} - (\text{Mean})^2 = \frac{454}{40} - (3.15)^2 = 11.35 - 9.9225 = 1.4275$ .
Standard Deviation = $\sqrt{1.4275} \approx 1.19$ (3 s.f.).
[3]

5.
(a) IQR Comparison:
$IQR_A = 55 - 25 = 30$ .
$IQR_B = 50 - 35 = 15$ .
Class A has the larger IQR.
[1]

(b) Consistency:
Class B has a smaller IQR (and smaller range), so Class B is more consistent.
OR
Class A has a larger spread, so Class A is less consistent.
[1]

6.
Total balls = $5 + 3 + 2 = 10$ .
(a) $P(\text{Red}) = \frac{5}{10} = \frac{1}{2}$ .
[1]
(b) $P(\text{Not Blue}) = 1 - P(\text{Blue}) = 1 - \frac{3}{10} = \frac{7}{10}$ .
[1]

7.
Sample space: $\{1, 2, 3, 4, 5, 6\}$ .
(a) Primes: $\{2, 3, 5\}$ . $P(\text{Prime}) = \frac{3}{6} = \frac{1}{2}$ .
[1]
(b) $> 4$ : $\{5, 6\}$ . $P(>4) = \frac{2}{6} = \frac{1}{3}$ .
[1]

8.
$P(\text{Not Rain}) = 1 - P(\text{Rain}) = 1 - 0.3 = 0.7$ .
[1]

9.
Mutually exclusive: $P(A \cup B) = P(A) + P(B)$ .
$P(A \cup B) = 0.4 + 0.25 = 0.65$ .
[1]

10.
Possibility Diagram:
Rows/Cols labelled 1-4.
16 outcomes listed/shown in grid.
[2]

11.
(a) Sum = 5: $(1,4), (2,3), (3,2), (4,1)$ . 4 outcomes.
$P(\text{Sum}=5) = \frac{4}{16} = \frac{1}{4}$ .
[1]
(b) Sum < 4: $(1,1), (1,2), (2,1)$ . 3 outcomes.
$P(\text{Sum}<4) = \frac{3}{16}$ .
[1]

12.
Sample Space: $\{HH, HT, TH, TT\}$ .
Exactly one Head: $\{HT, TH\}$ .
$P(\text{1 Head}) = \frac{2}{4} = \frac{1}{2}$ .
[2]

13.
$n(\text{Physics}) = 60$ , $n(\text{Chem}) = 50$ , $n(\text{Both}) = 20$ .
$n(\text{Physics only}) = 60 - 20 = 40$ .
$n(\text{Chem only}) = 50 - 20 = 30$ .
$n(\text{Neither}) = 100 - (40 + 30 + 20) = 10$ .

(a) $P(\text{Neither}) = \frac{10}{100} = \frac{1}{10}$ or $0.1$ .
[2]
(b) $P(\text{Physics only}) = \frac{40}{100} = \frac{2}{5}$ or $0.4$ .
[1]

14.
Total balls = 10.
(a) $P(WW) = \frac{4}{10} \times \frac{3}{9} = \frac{12}{90} = \frac{2}{15}$ .
[2]
(b) $P(WB \text{ or } BW) = \left(\frac{4}{10} \times \frac{6}{9}\right) + \left(\frac{6}{10} \times \frac{4}{9}\right) = \frac{24}{90} + \frac{24}{90} = \frac{48}{90} = \frac{8}{15}$ .
[2]

15.
$P(M) = 0.8$ , $P(S) = 0.7$ . Independent.
(a) $P(\text{Both}) = 0.8 \times 0.7 = 0.56$ .
[1]
(b) $P(\text{Exactly One}) = P(M \cap S') + P(M' \cap S)$ .
$P(M \cap S') = 0.8 \times (1-0.7) = 0.8 \times 0.3 = 0.24$ .
$P(M' \cap S) = (1-0.8) \times 0.7 = 0.2 \times 0.7 = 0.14$ .
Total = $0.24 + 0.14 = 0.38$ .
[2]

16.
Numbers 1-20.
$A = \{3, 6, 9, 12, 15, 18\}$ (6 numbers).
$B = \{2, 4, 6, 8, 10, 12, 14, 16, 18, 20\}$ (10 numbers).
$A \cap B = \{6, 12, 18\}$ (3 numbers).

(a) $P(A) = \frac{6}{20} = \frac{3}{10}$ .
[1]
(b) $P(A \cap B) = \frac{3}{20}$ .
[1]
(c) $P(A \cup B) = P(A) + P(B) - P(A \cap B) = \frac{6}{20} + \frac{10}{20} - \frac{3}{20} = \frac{13}{20}$ .
[1]

17.
Total marbles = 10. With replacement means probabilities remain constant.
(a) $P(RR) = \frac{3}{10} \times \frac{3}{10} = \frac{9}{100} = 0.09$ .
[1]
(b) $P(RB) = \frac{3}{10} \times \frac{7}{10} = \frac{21}{100} = 0.21$ .
[1]

18.
$\sum fx = (0\times5) + (1\times15) + (2\times20) + (3\times8) + (4\times2)$
$= 0 + 15 + 40 + 24 + 8 = 87$ .
Total days = 50.
Mean = $\frac{87}{50} = 1.74$ cars.
[2]

19.
(a) For normal distribution, probability within 1 SD is approx 0.68 (or 68%).
[1]
(b) Mean + 2 SD = $30 + 2(5) = 30 + 10 = 40$ cm.
[1]

20.
Total people = 10. Choosing 3.
Number of ways = $\binom{10}{3} = \frac{10 \times 9 \times 8}{3 \times 2 \times 1} = 120$ .
[2]