if the test scores in a class are normally distributed with a mean of 60 and a standard deviation of 4, then according to the 1-2-3 rule, 34% of students' scores would fall within what range? 60 to 68 52 to 68 60 to 64 60 to 72

Write the formulae  60% of all the students passed an exam. If a random sample of 10 students is selected, What is the mean and the standard deviation ?

The NJ Department of Health has reported the average life span of NJ residents is 81 years. If the standard deviation is σ = 4 years, what is the probability of a person living to at least 92 years of age?

A psychology teacher gave an objective-type test to a class of 400 students and, after seeing the results, decided that the scores were normally distributed. The mean score was 46, and the standard deviation was 15. The teacher assigned a grade of A to all scores of 76 or over, B to scores of 61 to 75, C to scores of 31 to 60, D to scores of 16 to 30 and F to scores below 16. About how many of each grade did the teacher assign? (Round your answers to the nearest whole number. Due to rounding, values may not add to the given sum. Recall that 34% of z-scores lie between 0 and 1, 13.5% lie between 1 and 2, and 2.5% are greater than 2.) A       B       C       D       F