JAMB 1990 · UME · Q48

The scores of a group of students in a test are shown. If the average score is 3.5, find the value of $x$ .

Score	1	2	3	4	5	6
No. of students	1	4	5	6	$x$	2

Worked solution (try it first)

Number of students: $1 + 4 + 5 + 6 + x + 2 = 18 + x$ .
Total score: $1 + 8 + 15 + 24 + 5x + 12 = 60 + 5x$ .
Mean = total ÷ number: $\frac{60 + 5x}{18 + x} = 3.5$ , so $60 + 5x = 63 + 3.5x$ .
Collect terms: $1.5x = 3$ , so $x = 2$ , option B.