The marks (out of 50) of 30 students in a…

The marks (out of 50) of 30 students in a science quiz are grouped below.

Question 25

MediumOriginal question

Marks	Number of students
0–10	4
10–20	7
20–30	12
30–40	5
40–50	2

The marks (out of 50) of 30 students in a science quiz are grouped below. Using class marks, what is the mean mark?

23Correct answerYour answer25Correct answerYour answer28Correct answerYour answer138Correct answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer A

Correct answer: A

Class marks: 5, 15, 25, 35, 45.
$\sum fx = 4 \times 5 + 7 \times 15 + 12 \times 25 + 5 \times 35 + 2 \times 45 = 20 + 105 + 300 + 175 + 90 = 690$ .
Mean = $\frac{690}{30} = 23$ .

Worth noting

25 is the average of the class marks, ignoring the frequencies. 28 uses the upper class limits instead of the class marks, and 138 divides by the 5 classes instead of 30 students.

Concept: Mean of grouped data by the direct method
Typical timeTypical: 70 s
Your timeYours: —

The rule this testsFrequency tables

Practise this chapter →

Ten questions from Mean, Median and Mode, at your own pace.

Practise this chapter →

Ten questions from Mean, Median and Mode, at your own pace.

The marks (out of 50) of 30 students in a science quiz are grouped below.

Question 25

Explanation