If you know the answer, please respond! I've been stuck on this question for the longest time
A fuel injection system is designed to last 18 years, with a standard deviation of 1.4 years. What is the probability that a fuel injection system will last less than 15 years?
A. 25%
B. 33%
C. 2%
D. 20%

C. 2%

Step-by-step explanation:

The question is asking the probability that the result is <15 years. The fuel injection system mean is 18 years with 1.4 years of standard deviation(SD). If you convert the desirable result into mean +/- SD it will be:

15 years = mean +/- x SD

15 years= 18 years +/-x 1.4 years

x= -3 years/1.4 years= - 2.14 SD

After this, you can find the z-score of -2.14 SD, which is 0.0162 = 1.62%. The closest answer is C.

Without the Z-score table, you can also predict the answer by using the 68-95-99.7 rule. Since its around 2SD away (2SD= 95%) and you only take -2 SD (not taking +2SD ), it will be  (100%-95%)/2= 2.5%

tube or goog would be a great resource to with that question