Question

A survey among freshmen at a large university showed that the number of hours spent studying the week before final exams was normally distributed with a mean of 25 hours and standard deviation of 7 hours. What is the probability a randomly selected freshman spends between 35 and 43 hours studying the week before final exams?

	a.	0.0565
	b.	0.8729
	c.	0.0713
	d.	0.1271

Answer 1

Solution :

Given that ,

mean = = 25

standard deviation = = 7

P(35 < x < 43) = P((35 - 25)/ 7) < (x - ) /  < (43 - 25) / 7) )

= P(1.43 < z < 2.57)

= P(z <2.57) - P(z < 1.43)

= 0.9949 - 0.9236 Using standard normal table,  

Probability = 0.0713

Option c is correct.