Answer:
138
Step-by-step explanation:
Population standard deviation = 
.95 probability of estimating the population mean monthly income within a margin of $20
So, Significance level = 1-0.95 = 0.05
α =0.05
Margin error = 20

Z at 0.05 = 1.96




So, n = 138
Hence sample size should be 138 selected to obtain a .95 probability of estimating the population mean monthly income within a margin of $20
Answer:
5
Step-by-step explanation:
5+12= 17
Answer:
No faster than 46 mph
Step-by-step explanation:
40*.15=6
6+40=46
(This is assuming they can go 15% over the speed limit and not that the car needs to be below 15% over the soeed limit)