Which expression is equivalent to 4x + 3 - 2x + 5.
2 answers:
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Answer:
a) 11.51%; b) 13 minutes
Step-by-step explanation:
We will use a z score to answer these questions. The formula for a z score is
For part a, X is 20, the mean is 17 and the standard deviation is 2.5:
z = (20-17)/2.5 = 3/2.5 = 1.2
Using a z table, we see the area to the left of, or less than, this value is 0.8849; this means the area to the right of, or greater than, is 1-0.8849 = 0.1151. This means 11.51% of people have a time greater than 20 minutes and get half off.
For part b, we start out in the z table finding values as close to 5%, or 0.05, as possible. There are two possibilities, 0.0505 (z=-1.64) and 0.0495 (z=-1.65). Since they are equally distant from the desired value, we will use -1.645 for z. Our values for the mean and standard deviation are the same:
-1.645 = (X-17)/2.5
Multiply both sides by 2.5:
2.5(-1.645) = ((X-17)/2.5)(2.5)
-4.1125 = X-17
Add 17 to each side:
-4.1125+17 = X-17+17
12.8875 = X
This means the garage should make the guaranteed time no more than 13 minutes.