Elementary statistics e-lesson week 9

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A survey found that women spend on average RM146.21 for the toiletries per month. Assume the standard deviation is RM29.44. Find the percentage of women who spend less than RM160.00. Assume the variable is normally distributed.

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A radar unit is used to measure speeds of cars on a motorway. The speeds are normally distributed with a mean of 90 km/hr and a standard deviation of 10 km/hr. What is the probability that a car picked at random is travelling at more than 100 km/hr?

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For a certain type of computers, the length of time between charges of the battery is normally distributed with a mean of 50 hours and a standard deviation of 15 hours. John owns one of these computers and wants to know the probability that the length of time will be between 50 and 70 hours.

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A large group of students took a test in Physics and the final grades have a mean of 70 and a standard deviation of 10. If we can approximate the distribution of these grades by a normal distribution, what percent of the students scored higher than 80?

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