(a) If we let x be the number of miles and y be the total cost, the equation for relating the number of miles and the total cost would be, y = 0.4x + 48
(b) If the rental cost is 60, 60 = 0.4x + 48 The value of x from the equation is 30.
(c) You may prepare the table of values by allowing x be any number and then solve for y until we arrive with an answer for y being equal to 60.
Problems of normally distributed samples are solved using the z-score formula.
In a set with mean and standard deviation , the zscore of a measure X is given by:
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
In this problem, we have that:
How often should the bulbs be replaced so that no more than 1% burn out between replacement periods?
This is the first percentile of hours. So it is X when Z has a pvalue of 0.01.