Question

The arithmetic mean of marks scored by 10 students was 20. Nikhil, one of the students, inquired other 9 students and recorded their deviation from his marks as -5, 6, 2, -2, 0, 2, 4, -3, 6. Find the marks of Nikhil.

• A. 15
• B. 17
• C. 19
• D. 21

Answer 1

The correct option is C 19

As we know,

Arithmetic mean = Estimated mean + Average of deviations

$Arithmeticmean=Estimatedmean+\frac{\text{Sum of deviations}}{\text{Number of Observations}}$

Let the marks of Nikhil = x.

As per the respective values given in question:

20 = x + $\frac{\text{-5+6+2-2+0+2+4-3+6+0}}{\text{10}}$

20 = x + $\frac{\text{10}}{\text{10}}$
20 = x + 1
x = 19