Standard deviation

Question

Terry is standing in line waiting for a snack. He will recieve one serving of chips and one serving of salsa. The amount of chips (in grams) per serving is a random variable with standard deviation 3.7. The amount of salsa (in grams) per serving is a random variable with standard deviation 2.8. The chips contain 5 calories per gram and the salsa contains 0.5 calories per gram. The amounts of the two snacks that Terry receives can be considered to be independent. What is the standard deviation (in grams) of the total number of calories Terry receives?

 

 a) 4.46

b) 8.51

c) 18.55

d)19.90

e)344.21

 

Answer 1

A) is the closest and I bet the digits in that number are backwards... I got 4.64

 

 Because of the independence ,    the formula for the combined standard-deviation is:

 

     square-root (   std-dev1 ^2  +  std-dev2 ^2 ) =

 

    square-root  ( 3.7 * 3.7 + 2.8 *2.8 ) = 4.64