Ex 14.1, 8 (Method 1 – Direct Method)
A class teacher has the following absentee record of 40 students of a class for the whole term. Find the mean number of days a student was absent.
Here Class Size is not same,
So, we solve by Direct Method
Putting values in formula
Mean(𝑥 ̅) = (∑▒𝑓𝑖𝑥𝑖)/(∑▒𝑓𝑖)
𝑥 ̅ = 499/40
𝒙 ̅ = 12.48
Therefore, Mean number of days a student was absent is 12.48 daysEx 14.1, 8 (Method 2 – Step Deviation Method)
A class teacher has the following absentee record of 40 students of a class for the whole term. Find the mean number of days a student was absent.
Here Class Size is not same…
So, in Step Deviation Method
Mean(𝑥 ̅) = a + h × (∑▒𝒇𝒊𝒖𝒊)/(∑▒𝒇𝒊)
We use a value of h which can divide
𝑑𝑖 = 𝑥𝑖 − a
Mean(𝑥 ̅) = a + h × (∑▒𝒇𝒊𝒖𝒊)/(∑▒𝒇𝒊)
Where
a = Assumed Mean
Let h = Class interval
Also,
∑▒𝒇𝒊 = 40
∑▒𝒇𝒊𝒖𝒊 = −90.5
Putting values in formula
Mean(𝒙 ̅) = a + h × (∑▒𝒇𝒊𝒖𝒊)/(∑▒𝒇𝒊)
𝑥 ̅ = 17 + 2 × (−90.5)/40
𝑥 ̅ = 17 – 4.525
𝒙 ̅ = 12.475
Therefore, Mean number of days a student was absent is 12.48 days

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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