Tire pressure monitoring systems are increasingly common for vehicles, but such systems rarely include checking the spare tire. The article “A Statistical Study of Tire Pressures on Road-Going Vehicles” (SAE Intl. J. Passeng. Cars—Mech. Systems 2016) provided the following data on the amount (psi) by which spare tires in a sample of 95 cars were under-inflated, relative to manufacturer’s specifications:

a. What does a value of 0 represent here? What does a negative value represent?
b. Construct a relative frequency histogram based on the class boundaries –20, –10, 0, 10,…, 50, and 60, and comment on features of the distribution.
c. Construct a histogram based on the following class boundaries: −20, 0, 10, 20, 30, 40, and 60. 

d. What proportion of spare tires in the sample were within ± 10 psi of their manufacturer-recommended pressure?

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29 58 -6 15 4 8 16 -5 35 11 25 20 46 5 0 50 20 39 30 -12 60 57 7 60 40 52 -6 19 32 4 60 29 19 32 12 30 8 25 42 35 9 -11 50 41 12 50 38 32 0 42 29 13 37 13 10 10 5 3 16 20 7 17 34 23 57 50 6 6 51 41 20 15 25 52 46 16 60 5 57 1 54 -3 26 35 1 24 52 55 57 31 41 20 45 0 25