You run a house flipping business where you buy thousands of houses across the country, hire contractors to fix them up, and try to sell them. For any given house, you figure there is a 50%/50% chance...

You run a house flipping business where you buy thousands of houses across the country, hire contractors to fix them up, and try to sell them. For any given house, you figure there is a 50%/50% chance of gaining 60% or losing 40%. This means your expected return per house is 0.5x0.60+0.5x(-0.40) = 0.10 = 10%. The variance per house is 0.5x(0.60-0.10)2 + 0.5x(-0.40-0.10)2 = 0.25. If the covariance between houses is 0.10, what is the variance of your portfolio of thousands of houses