There are 32 students in an elementary statistics class. On the basis of years o
ID: 3318986 • Letter: T
Question
There are 32 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 7 min and a standard deviation of 5 min. (Give answers accurate to 3 decimal places.) 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 PM. 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?Explanation / Answer
a) here expected time to grade all students =32*7=224
and std deviation=5*(32)1/2 =28.2843
hence probability that he will grade all with in 250 min =P(X<250)=P(Z<(250-224)/28.2843)=P(Z<0.9192)=0.8210
b) P(X>260)=P(Z>(260-224)/28.2843)=P(Z>1.2728)=0.1015
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