Answer:
0.336
Step-by-step explanation:
Here the mean is 83 min and the standard deviation is 33 minutes. Â Note that
1 standard deviation above the mean comes out to (83 + 33) minutes, or 116 minutes. Â So 97 minutes is above the mean and below 1 standard deviation above the mean.
What is the probability that the interval is BELOW 97 minutes? Â If we find this, subtracting it from 1.000 results in the desired probability.
Using the Distribution key on my TI 83 Plus calculator, I get:
normalcdf(-100,97, 83,33) = 0.664. Â
Subtracting this from 1.000 results in 0.336.
Tthe probability that a randomly selected time interval between eruptions is longer than 97 minutes is thus 0.336.