Question

PLEASE HELP


The time required to finish a test in normally distributed with a mean of 80 minutes and a standard
deviation of 15 minutes. What is the probability that a student chosen at random will finish the test in more
than 95 minutes?

Answer 1

First: a quick-and-dirty approach:

1) Recognize that 95 is one standard deviation above the mean (80)
2) One standard deviation above the mean corresponds to a z-score of 1.
3) Look up z=1 on the left margin of a table of standard normal probability values and find the corresponding probability (area). That will be the area TO THE LEFT OF z=1.
4) Subtract this area from 1.0000. The result is the probability that you wanted.

If any step of this process is unclear for you, ask for clarification. Likewise, if you'd like more details, just ask.

Answer 2

Uhh, what do you mean by a table of standard normal probability values, sorry, my course didn't teach me this :P

Answer 3

Very sorry for the delay in responding to your question.
If you have not learned how to use "a table of std. normal probability," then have you heard of and studied the Empirical Rule?

Answer 4

The Empirical Rule states that 68% of all normally-distributed data lies within ONE STANDARD DEVIATION of the mean, 95% within 2 std. devs. and 99.7% within 3 std. devs.

If you have seen this before, let me know. In either case, I'll give you more information about this rule that will enable you to answer your posted question properly.

Answer 5

Yes that is what my course has taught me, sorry for late reply.

Answer 6

Good morning! 95 is how many std. devs. above the mean? (Just a review.)

Answer 7

Hint: 80 + 1(15) = ?

Answer 8

@bankiwi: Are you with me or not? Happy to help, but I'd like to get this particular problem done as quickly as possible.

Answer 9

its 1 standard deviation