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  • Calculate the mean of the scores of 20 students in a mathematics test :

Calculate the mean of the scores of 20 students in a mathematics test :

Marks 10-20 20-30 30-40 40-50 50-60
Number of students 2 4 7 6 1

                       

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best_answer

Answer.  [35]

Solution.   Here we calculate mean by following the given steps:

  1. Find the mid point of each interval.
  2. Multiply the frequency of each interval by its mid point.
  3. Get the sum of all the frequencies (f) and sum of all  the (fx)
    4     Now divide sum of (fx) by sum of (f)
Marks xi No.of students fi fixi
10-20 15 2 30
20-30 25 4 100
30-40 35 7 245
40-50 45 6 270
50-60 55 1 55

 \sum f_{i}= 20      \sum f_{i}x_{i}= 700

mean\left ( \bar{x} \right )= \frac{\sum f_{i}x_{i}}{\sum f_{i}}= \frac{700}{20}= 35

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