The time required to finish a test in normally distributed with a mean of 40 minutes and a standard deviation of 8 minutes. What is the probability that a student chosen at random will finish the test in between 32 and 56 minutes?

Question

anonymous · Answer

Well I got a warning from the moderator in the last post for answering your question, so this time I will just guide you and not give you the answer. Use the z-score formula (point - mean)/standard deviation. Get the z-scores for both the points 32 and 56.

That is the first step. Do this and then tell me what z-scores you get.

anonymous · Answer

By the way do you know the 68 95 99.7 rule? It's a good rule to know when you are calculating z-scores on a normal distribution. There's an article of it on Wikipedia that will provide you a good explanation of the rule.

anonymous · Answer

is it 82% ?

anonymous · Answer

Close, I got 81.5% but if you're rounding up then yes 82%.

I got 81.5% because 32 is 1 standard deviation below 40 which means 16% of students finish the test before 32 minutes. 56 minutes is 2 standard deviations above 40, meaning 2.5% of students finish the test after 56 minutes. So to get the percent of people between 32 and 56 I added 16+2.5 = 18.5 and then do 100-18.5 = 81.5%

anonymous · Answer

yeah I have to round up thanks for confirming?

anonymous · Answer

You're welcome, hope the mod doesn't get pissed at me again lol.

anonymous · Answer

lol