1) The waiting times at a certain bank are normally distributed with a mean wait

Question

1) The waiting times at a certain bank are normally distributed with a mean waiting time of 3.7 minutes and a standard deviation of 1.4 minutes. Find the waiting time at the 97th percentile. That is, find the wait time that separates the bottom 97% from the rest.

Select one:

a. .02

b. .97

c. 1.9

d. 6.3

2) Scores on a recent NYS Standardized Exam were normally distributed with a mean of 77.6 and a standard deviation of 4.3.

Find the NYS Standardized Exam score that separates the bottom 2.5% from the rest. Round this score to the nearest tenth.

Select one:

a. -1.96

b. 69.2

c. 1.96

d. 75.3

3) Assume that readings on thermometers are normally distributed with a mean of 0 and a standard deviation of 1. A thermometer is selected at random. Find the probability that the reading is between -1.25 and -.05.

Select one:

a. .9068

b. .5857

c. .3745

d. .2029

4) Scores on a recent NYS Standardized Exam were normally distributed with a mean of 77.6 and a standard deviation of 4.3.

Find the probability that the mean of a randomly chosen sample of 25 students scores is between 72.3 and 79.8.

Select one:

a. .9947

b. .9948

c. .0001

d. .0256

5) The average credit card debt for college seniors is $3262. If the debt is normally distributed with a standard deviation of $1100, find the probability that a group of 36 seniors will owe more than a mean of $4000?

Select one:

a. .9999

b. .0001

c. .2514

d. .8413

Explanation / Answer

1) 97th Percentile = NORMSINV(0.97)*1.4+3.7 = 6.3

2) 97th Percentile = NORMSINV(0.025)*4.3+77.6 = 69.2

3) P(-1.25<z<-0.05)

= NORMSDIST(-0.05)-NORMSDIST(-1.25)

= 0.3745

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