The marks of the candidates in a school test are grouped in the table below…

Contributed by StemPy Lab

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

The marks of the candidates in a school test are grouped in the table below. The frequency of the class $60$ to $80$ is missing, and we call it $x$ . The number of candidates is not given either. The only clue is that the mean mark of all the candidates was $52$ . Use it to find $x$ , and then the number of candidates.

Marks	Candidates
0-20	4
20-40	8
40-60	13
60-80	$x$
80-100	5

Find $x$ , and the number of candidates.

Need a reminder? The key ideaShow

Name the missing frequency $x$ , write the clue as a formula in $x$ , solve, and check. For the mean, use $\bar{x} = \dfrac{\sum fx}{N}$ with both $\sum fx$ and $N$ in terms of $x$ . For the median, decide the median class first. A frequency is a whole number that is not negative.

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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