3. The time it takes girls aged 15 to complete an obstacle course is found to be normally distributed with a mean of 21.5 minutes and a standard deviation of 2.2 minutes.
- Find the probability that a randomly chosen 15 year-old girl completes the course in less than 25 minutes.
A 13 year-old girl completes the course in exactly 19 minutes.
- What percentage of 15 year-old girls would she beat over the course?
Anyone completing the course in less than 20 minutes is presented with a certificate of achievement. Three friends all complete the course one afternoon.
- What is the probability that exactly two of them get certificates?