There are 40 students in an elementary statistics class. On the basis of years o
ID: 3318869 • Letter: T
Question
There are 40 students in an elementary statistics class. On the basis of years of experience, the instructor knows that the time needed to grade a randomly chosen first examination paper is a random variable with an expected value of 6 min and a standard deviation of 7 min. (Give answers accurate to 3 decimal places.) (a) If grading times are independent and the instructor begins grading at 6: 50 PM. and grades continuously, what is the (approximate) probability that he is through grading before the 11:00 P.M. TV news begins? (b) If the sports report begins at 11:10, what is the probability that he misses part of the report if he waits until grading is done before turning on the TV? You may need to use the appropriate table in the Appendix of Tables to answer this questionExplanation / Answer
a)expected time to grade 40 students =40*6=240
and std deviaiton=7*(40)1/2 =44.27
a) probability that he will be through in 250 minuites =P(X<250)=P(Z<(250-240)/44.27)=P(Z<0.2259)=0.5894~ 0.589
b)
probability =P(X>260)=1-P(X<260)=1-P(Z<(260-240)/44.27)=1-P(Z<0.4518)=1-0.6743=0.3257 ~ 0.326
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.