Answer:
2.35%
Step-by-step explanation:
Mean number of months (M) = 39 months
Standard deviation (S) = 10 months
According to the 68-95-99.7 rule, 95% of the data is comprised within two standard deviations of the mean (39-20 to 39+20 months), while 99.7% of the data is comprised within two standard deviations of the mean (39-30 to 39+30 months).
Therefore, the percentage of cars still in service from 59 to 69 months is:
[tex]P_{59\ to\ 69}=\frac{P_{9\ to\ 69}-P_{19\ to\ 59}}{2} \\P_{59\ to\ 69}=\frac{99.7-95}{2}\\P_{59\ to\ 69}=2.35\%[/tex]
The approximate percentage of cars that remain in service between 59 and 69 months is 2.35%.
