could you define covariance? I know I could look it up, but maybe if you explain what it is, it'll help with your understanding.

However, you can show that with a system of linear equations:

x (amount invested in A)

y (amount invested in B)

.12x + .10y = .11 (x+y)

.01x - .01y = 0

x - y = 0

x = y

so the man invested equal amounts in A and B.

Ask if you need more help, although I haven't yet taken a university stats.