Explanation : Add one to each of the given returns, then multiply them together, then
take the fifth root of the resulting product. 1.18 × 1.12 × 0.95 × 0.90 ×
1.07 = 1.209066. 1.209066 raised to the 0.20 power is 1.0387.
Subtracting one and multiplying by 100 gives the correct geometric
mean return of 3.87%.