# statistics

posted by .

According to a bank, the time taken by its customers to use cash dispensing machines is normally distributed with a mean of 18 seconds and a standard deviation of 3 seconds.
I) What is the probability that a customer selected at random takes less than 13 seconds?
II) Find the proportion of customers that take :
a) Between 15 and 21 seconds to use the cash dispensers?
b) Between 12 and 24 seconds to use the cash dispensers?

• statistics -

Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores.

## Similar Questions

1. ### statistics

The time it takes to give a man a shampoo and haircut is normally distributed with a mean of 22 minutes and standard deviation of 3 minutes. Customers are scheduled every 30 minutes. (a) What is the probability that a male customer …
2. ### Statistics

If a completion time for a task is normally distributed with a mean of 15 seconds and a standard deviation of 2.5 seconds, what is the probability of getting a time less than 9.7 seconds?
3. ### statistics

The reaction time of subjects to a certain psychological experiment is considered to be normally distributed with a mean of 20 seconds and a standard deviation of 4 seconds. What is the reaction time such that only 10% of subjects …
4. ### statistics

The reaction time of subjects to a certain psychological experiment is considered to be normally distributed with a mean of 20 seconds and a standard deviation of 4 seconds. What is the reaction time such that only 10% of subjects …
5. ### Statistics

Problem During the dinner hour, the distribution of the inter-arrival time of customers at a restaurant is estimated to be as shown below. The mode of payment and the service times of the cash and credit card customers are shown in …
6. ### statistics

The length of country and western songs is normally distributed and has a mean of 200 seconds and a standard deviation of 30 seconds. Find the probability that a random selection of 9 songs will have mean length of 186.30 seconds or …
7. ### fnu

The length of country and western songs is normally distributed and has a mean of 200 seconds and a standard deviation of 30 seconds. Find the probability that a random selection of 9 songs will have mean length of 186.30 seconds or …
8. ### Statistics

ATM transaction times are normally distributed with a mean of 150 seconds and a standard deviation of 45 seconds. What is the probability a person takes less than 60 seconds to complete their transaction?