Answer:
SD = 0.0740270 or 7.40270 percent rounded off to 7.403 percent
Explanation:
To calculate the standard deviation of the investment, we must first calculate the expected or mean return of the investment. The expected or mean return can be calculated as follows,
r = pA * rA + pB * rB + ... + pN * rN
Where,
r = 0.2 * 0.16 + 0.4 * 0.12 + 0.2 * 0.05 + 0.2 * -0.05
r = 0.08 or 8%
The formula to calculate the standard deviation of a stock/investment is as follows,
SD = √pA * (rA - r)² + pB * (rB - r)² + ... + pN * (rN - r)²
SD = √0.2 * (0.16 - 0.08)² + 0.4 * (0.12 - 0.08)² + 0.2 * (0.05 - 0.08)² + 0.2 * (-0.05 - 0.08)²
SD = 0.0740270 or 7.40270 percent rounded off to 7.403 percent