SOLUTION: I'm not sure if this is the right section, but this question is about the normal distribution: Tony is training for the athletic sports. He has found that 70% of the times he reco

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Question 358978: I'm not sure if this is the right section, but this question is about the normal distribution:
Tony is training for the athletic sports. He has found that 70% of the times he records are less than 56.3 seconds and 20% are less than 52.3 seconds. If the times he records are normally distributed then what are mean and the standard deviation of his times?
Thanks in advance.
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Reading off from a standard normal table, and using the formula Z+=+%28X+-+mu%29%2Fsigma, we get the system
matrix%282%2C1%2C+-0.845+=+%2852.3+-+mu%29%2Fsigma%2C+0.525+=+%2856.3+-+mu%29%2Fsigma%29.
Solving for mu and sigma, we should get
mu+=+54.767, and sigma+=+2.92.