Risk of the portfolio = Square root of (WA^2 * Sa^2 + Wb^2 * Sb^2 + 2 Wa * Wb * Sa * Sb * Correlation coefficient)
Wa – Weight of Security A = 0.5 (50%)
Wb – Weight of Security B = 0.5 (50%)
Sa – Std deviation of A = 0.15
Sb – Std deviation of B = 0.2
Correlation coefficient = 0.5
Portfolio risk = Square root of (0.5*0.5*0.15*0.15)+(0.5*0.5*0.2*0.2)+(2*0.5*0.5*0.15*0.2*0.5)
Portfolio risk = 0.152069063
Portfolio risk (Portfolio Std deviation) = 15.2%