He will have 7.75 left from the 20 dollar bill he spent
We have been given that the standard deviation of a group of 20 scores is 15 and we are asked to find variance.
Since we know variance is square of standard deviation. In order to find out the variance of the given data we have to take the square of 15.

Therefore, our variance is 225.
Answer:
There is an 84.97% probability that at least six wear glasses.
Step-by-step explanation:
For each adult over 50, there are only two possible outcomes. Either they wear glasses, or they do not. This means that we use the binomial probability distribution to solve this problem.
Binomial probability distribution
The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

In which
is the number of different combinatios of x objects from a set of n elements, given by the following formula.

And p is the probability of X happening.
In this problem we have that:

What is the probability that at least six wear glasses?

There is an 84.97% probability that at least six wear glasses.
Answer: Choice A
Ahmed started 6 floors above ground level, then he went down 8 floors
The +6 or simply 6, is positive, so he's on the 6th floor to start. Then adding on -8, which is the same as subtracting 8, moves him down 8 floors.
6 + (-8) = 6 - 8 = -2 indicates he's 2 floors below ground level, so he's in basement level 2 (perhaps some kind of parking garage).
The formula for the volume of a quarter-sphere is simply one-fourth of the volume of the sphere. So the volume of a quarter-sphere:
V = (1/4) (4/3) (π r³)
or
V = (1/3) (π r³)
Since we are given with the radius of 70 feet, the volume is
V = (1/3) (π) (70³)
V = 359,189 cubic feet