Q10 of 33 Page 156

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.

Let Karishma got 'a' marks.

And assumed mean be 'a'.


We know,


Arithmetic mean,


Where, a is assumed mean.


As, deviations given are -8, -6, -3, -1, 0, 2, 3, 4, 6


Sum of deviations = -8 + (-6) + (-3) + (-1) + 0 + 2 + 3 + 4 + 6


= -3


As, arithmetic mean of marks is 15


Putting values in formula, We have,



⇒ 15 = a - 0.3


⇒ a = 15.3


⇒ Karishma got 15.3 marks


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