The average time taken to complete a test follows normal probability distribution with a mean of 70 minutes and a standard deviation of 25 minutes.
The probability of a randomly selected student completing the test in 45 minutes or less is approximately equal to ____%. The probability of a randomly selected student completing the test in 95 minutes is _____%.

Question

The average time taken to complete a test follows normal probability distribution with a mean of 70 minutes and a standard deviation of 25 minutes.
The probability of a randomly selected student completing the test in 45 minutes or less is approximately equal to ____%. The probability of a randomly selected student completing the test in 95 minutes is _____%.

vocaloid · Answer

calculate the z-score for 45 minutes and 95 minutes using the formula

z-score = (x - mean)/standard deviation

then use either a z-table or a calculator to calculate the percentages