X is normal with mean 120 mm and standard deviation 0.3 mm; Y is independent and normal with mean 80 mm and standard deviation 0.4 mm. Find the standard deviation σ of the difference X − Y.
Drag z so that the shaded area under the standard normal curve, to the left of z, is 0.7357. Find z to two decimals.
The masses of passengers with luggage are independent and normal with mean 85 kg and standard deviation 12 kg. Find the probability P that the total mass of 4 of them exceeds 304 kg. Round z to two decimals.
Drag z so that the shaded area between −z and z under the standard normal curve is 0.3899. Find z to two decimals.
The exam scores are normally distributed with mean 65 points and standard deviation 10 points. Drag the cut-off so the shaded bottom 30% is to the left of it. Find the cut-off x.
The exam scores are normally distributed with mean 65 points and standard deviation 10 points. Find the value x below which 10% of them lie (the 10th percentile).
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