Question 31

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Jambmaths question: 

Scores

1

2

3

4

5

6

No of students

1

4

5

6

x

2

The table above shows the score of a group of students in a test. If the average is 3.5, find the value of x

Jamb Maths Solution: 

$\begin{align}  & \overline{x}=\frac{\sum f(x)}{\sum f} \\ & 3.5=\frac{(1\times 1)+(2\times 4)+(3\times 5)+(4\times 6)+(5\times x)+(6\times 2)}{1+4+5+6+x+2} \\ & 3.5=\frac{1+8+15+24+5x+12}{18+x} \\ & \frac{7}{2}=\frac{60+5x}{18+x} \\ & 7(18+x)=2(60+5x) \\ & 126+7x=120+10x \\ & 126-120=10x-7x \\ & 6=3x \\ & x=2 \\\end{align}$

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