In a recent study, 55% of the cars tested failed the safety test. if 231 cars failed the safety test, how many cars were tested

What is the range? can’t seem to find it out

Given: m zade = 60° and m2cdf = (3x + 15) prove: x = 15

The ages of personnel in the accounting department of a large company are normally distributed with a standard deviation of 7 years. there is a 0.02275 probability that the age of any randomly chosen person in the department is less than 22 and 0.15866 probabilty that the age of any randomly chosen person is greater than 43. what is the mean of this distribution?