If the covariance between two investments of a portfolio is zero,the variance of the portfolio will be equal to the sum of the variances of the investments.

Covariance

A measure indicating the extent to which two variables change in tandem.

Variances

Statistical measures that represent the extent to which a set of numbers is spread out from their average value.

Portfolio

A grouping of investment tools like equities, bonds, raw goods, actual cash, and assets similar to cash, which also comprises mutual funds and ETFs.