Stuck on a simple problem

#1
The problem is as follows: The amount of money bob earns has an expected value of $30,000 and a standard deviation of $3000. The amount fo money that his wife sandy earns has an expected value of $32,000 and and standard deviation of $5000. Determine the values eanring of this families:

a) expected value
b) standard deviation


I have been told that these are independant and I have calculated the variance for part B but still cannot figure out what to do next.
 

JohnM

TS Contributor
#2
For independent variables:

(a) the total expected value is the sum of the individual expected values

(b) the total standard deviation is the square root of the sum of the individual variances
 
#3
Thanks for the help I think I was actually doing it all wrong, I have the mean to be $31,000 and the square root of that to be $176.07. Now do I subtract that number by the Standard deviations given then add those and divde by 2 to find my overal S.D?

Also for part A is $63,000 correct? It seemed like it was a bit to easy.
 

JohnM

TS Contributor
#4
midvinter said:
Thanks for the help I think I was actually doing it all wrong, I have the mean to be $31,000 and the square root of that to be $176.07. Now do I subtract that number by the Standard deviations given then add those and divde by 2 to find my overal S.D?

Also for part A is $63,000 correct? It seemed like it was a bit to easy.
part a is correct.

for part b, square each standard deviation, then add them together, and take the square root of the sum.