SOLUTION: Typing speed on a new kind of keyboard for people at a certain stage in their training program is approximately normally distributed. The probability that the speed of a given trai

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Question 465609: Typing speed on a new kind of keyboard for people at a certain stage in their training program is approximately normally distributed. The probability that the speed of a given trainee will be greater than 65 words per minute is 0.45. The probability that the speed will be more than 70 words per minute is 0.15. Find the mean and the standard deviation of typing speed.
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Typing speed on a new kind of keyboard for people at a certain stage in their training program is approximately normally distributed. The probability that the speed of a given trainee will be greater than 65 words per minute is 0.45. The probability that the speed will be more than 70 words per minute is 0.15. Find the mean and the standard deviation of typing speed.
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Find the z-value with a right tail of 0.45: invNorm(0.55) = 0.1257
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Find the z-value with a right tail of 0.15: invNorm(0.85) = 1.0364
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Solve for "u" using x = zs+u
65 = 0.1257s + u
70 = 1.0364s + u
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Subtract and solve for "s":
5 = 0.9107s
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s = 5.49
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Solve for "u":
5 = 0.1257*5.49 + u
u = 4.31
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Cheers,
Stan H.