Answer:
10.56%
Step-by-step explanation:
Finishing times by competitive male runners age 15-18 for the tough 5K race are approximately normally distributed with a mean of 18 + 4.5 = 22.5 minutes and a standard deviation of 2 minutes. (Adding 4.5 minutes to each runner’s time does not affect the standard deviation of the finishing times.) Using technology: normalcdf(lower: 25, upper: 10000, mean: 22.5, SD: 2) = 0.1056, so about 10.56% of competitive male runners in the 15-18 age bracket typically do not earn a completion medal at this race. Using z-scores and Table A: z = (25 – 22.5)/2 = 1.25. The area to the left of z = 1.25 is 0.8944, so the area to the right of z = 1.25 is 1 – 0.8944 = 0.1056 or 10.56%.