The times of all 15 year olds who run a certain race are approximately normally distributed with a given mean mu is equal to 18 sec and standard deviation sigma is equal to 1 point 2 sec. What percentage of the runners have times less than 14 point 4 sec?

Convert 14.4 seconds to a z-score: (14.4 − 18) ÷ 1.2 = −3. A time 3 standard deviations below the mean is in about 0.15% of a normal distribution’s lower tail. Therefore, about 0.15% of the runners have times below 14.4 seconds, which is choice A.

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