# standard deviation in probabilty??? help

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• Apr 29th 2009, 11:45 AM
arslan
standard deviation in probabilty??? help
Miguel buys a large bottle and a small bottle of juice. The amount of juice that the manufacturer puts in the large bottle is a random variable with a mean of 1024 ml and a standard deviation of 12 ml. The amount of juice that the manufacturer puts in the small bottle is a random variable with a mean of 506 ml and a standard deviation of 3 ml. If the total amount of juice in the two bottles can be described by a normal model, what's the probability that the total amount of juice in the two bottles is more than 1548.6 ml?
• Apr 29th 2009, 07:54 PM
mr fantastic
Quote:

Originally Posted by arslan
Miguel buys a large bottle and a small bottle of juice. The amount of juice that the manufacturer puts in the large bottle is a random variable with a mean of 1024 ml and a standard deviation of 12 ml. The amount of juice that the manufacturer puts in the small bottle is a random variable with a mean of 506 ml and a standard deviation of 3 ml. If the total amount of juice in the two bottles can be described by a normal model, what's the probability that the total amount of juice in the two bottles is more than 1548.6 ml?

The mean of the normal distribution is 1024 + 506 and the variance is 12 + 3.

Now calculate Pr(X > 1548.6).
• Apr 30th 2009, 04:24 AM
arslan
Quote:

Originally Posted by mr fantastic
The mean of the normal distribution is 1024 + 506 and the variance is 12 + 3.

Now calculate Pr(X > 1548.6).

thank you for your help but how do i go about calculating Pr(X > 1548.6) i am confused and new to this variable stats.
• Apr 30th 2009, 06:18 AM
mr fantastic
Quote:

Originally Posted by arslan
thank you for your help but how do i go about calculating Pr(X > 1548.6) i am confused and new to this variable stats.

You know X ~ normal(mean = 1024 + 506, variance = 12 + 3). And you should have been taught how to calculate probabilities that follow a normal distribution. So where are you stuck in finding Pr(X > 1548.6)?