# Thread: Joint Normal distributed independent random variable question

1. ## Joint Normal distributed independent random variable question

Sam's bowling scores are approximately normally distributed with mean 110 and standard deviation 11, while John's scores are normally distributed with mean 145 and standard deviation 10. If Sam and John each bowl one game, then assuming that their scores are independent random variables, approximate the probability that the total of their scores is above 240.

I have tried alot of things.

Here is what i recently have

i added the two means together which is 255 and added the standard deviation together whch is 21.

I then threw that into the f(x) equation for a normally distribution random variable. I believe 1-f(240) should give me the correct answer, but it is not.

Edit: i got the right answer. I used the integral from 0 to 240 !

2. ## Re: Joint Normal distributed independent random variable question

Standard deviations aren't additive like that. Variances are. Are you sure you got the right answer?

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