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ICSEClass 10MathematicsMeasures Of Central Tendency03 Mark2024 Moderate

QQuestion

The following table gives the duration of movies in minutes:

Duration (minutes) Number of movies
100–110 5
110–120 10
120–130 17
130–140 8
140–150 6
150–160 4

Using the step-deviation method, find the mean duration of the movies.

Exam-ready answer • 03 Mark

Answer

Class width, i = 10. Take the assumed mean A = 135.

Class Class mark x d = x − A u = d/i f fu
100–110 105 −30 −3 5 −15
110–120 115 −20 −2 10 −20
120–130 125 −10 −1 17 −17
130–140 135 0 0 8 0
140–150 145 10 1 6 6
150–160 155 20 2 4 8

Σf = 50 and Σfu = −38

Mean = A + \frac{\Sigma fu}{\Sigma f}\times i

⇒ Mean = 135 + \frac{-38}{50}\times10

⇒ Mean = 135 − 7.6

⇒ Mean = 127.4 minutes

Therefore, the mean duration is 127.4 minutes.

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