The standard deviation of a sample of 100 observations equals 64. the variance of the sample equals:

In general we know standard deviation is a measure of how the numbers are spread out.

And variance is the average of squared difference from mean.

So the relation between variance and standard deviation is as given below:

Standard deviation is the square root of variance.
So we can say variance is the whole square of standard deviation.

In given question standard deviation is 64.

So the variance will be square of 64.
Variance =
                =
So the variance of given 100 observation is 4096

The correct answer is 7