#### Answer

a. sample
b. mean = 19.46
variance = 44.04
standard deviation = 6.6363

#### Work Step by Step

a. Because the frequency given are only for the computers sold at an electric shop, it represents only a sample.
b. Mean =$∑fx\div n$ = $486.5/25$=19.46
Variance = =$(∑(fx)^2 - ([(∑fx)]^2/N))/(n-1)$
= $\frac{10524.25-(236682.3\div25)}{24}$
=$(10524.25-9467.29)\div24$
=44.04
Standard deviation = $\sqrt 44.04 = 6.6363 $