Q8 of 33 Page 156

If sum of the 20 deviations from the mean is 100, then find the mean deviation.

Given, No of deviations = 20

Sum of deviations = 100


We know,


Mean deviation


⇒ Mean deviation


⇒ Mean deviation = 5


Hence, mean deviation is 5.


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Two years ago the mean age of 40 people was 11 years. Now a person left the group and the mean age is changed to 12 years. Find the age of the person who left the group.

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Find the sum of deviations of all observations of the data 5, 8, 10, 15, 22 from their mean.

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Marks of 12 students in a unit test are given as 4, 21, 13, 17, 5, 9, 10, 20, 19, 12, 20, 14.

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Arithmetic mean of marks (out of 25) scored by 10 students was 15. One of the student, named Karishma enquired the other 9 students and find the deviations from her marks are noted as − 8, − 6, − 3, − 1, 0, 2, 3, 4, 6. Find Karishma’s marks.