Calculations-With-The-Mean Wjec-Eduqas Foundation

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Exam code:C300

Calculations with the mean

Remember what the mean is
- Mean = total of values ÷ number of values
  - It is a formula involving three quantities
  - if you know any two, you can find the other one
A question may require you to work backwards from a known mean
- It helps to rearrange the formula
- Total of values = mean × number of values
Find the total of the values before and after to help with question that involve:
- missing values
- adding in, or taking out, a value

It helps to start thinking of the mean as a formula which you can rearrange
- Total of values = mean × number of values

A class of 24 students has a mean height of 1.56 metres.
A new student joins the class.
The mean height of the class is now 1.57 metres.

Find the height of the new student.

Rearrange the formula for mean to get ‘total of heights = mean height × number of students’
Find the total of heights before

Total of heights before = 1.56 × 24 = 37.44

Find the total of heights after
Remember there are now 25 students

Total of heights after = 1.57 × 25 = 39.25

The height of the new student is the difference of the two totals above

39.25 – 37.44 = 1.81

The height of the new student is 1.81 metres