(a) Company D has the least variability because it has the smallest range.
(b) Company A has the highest salaries, on average, because it has the largest mean salary.
If you just type that exact equation into a calculator it gives you the same answer as well
2x-13+13=13-8x+14+13
2x=40-8x
2x+8x=40-8x+8x
10x=40
X=4
nCr(20, 2) = 190 ways of selecting 2 from 20
nCr(10, 1) = 10 ways of selecting 1 from 10
To find the over all probability of winning,
Calculate the Harmonic Mean (19) and divide by 2
Equivalent to
1/ (1//190 + 1/10) =9.5
So the probability is 1/9.5 = 2/19.