Answer:
The standard deviation is 17.5
Step-by-step explanation:
Let S be the sum of X and Y
S = X + Y
So we want to calculate the standard deviation of S
The standard deviation of S will be the square root of the sum of the variances of X and Y
Kindly recall that variance is the square of standard deviation
The variance of X will be 15^2 = 225
The variance of Y will be 9^2 = 81
So the standard deviation of the sum will be
√(81 + 225)
= √(306)
= 17.5
