Final answer:
The prefix indicating an abnormally high rate of speed is 'hyper-'. In running, it's more desirable to have a speed with a high percentile, with high percentile implying faster speed. If the 40th percentile speed is 7.5 mph, it means 40% of runners are at or below this speed.
Step-by-step explanation:
The prefix that indicates an abnormally high rate of speed in English is 'hyper-'. The prefix 'hyper-' comes from Greek and means 'over', 'beyond', or 'above'. It is often used to create words that describe something as excessively high or above normal. For example, 'hypersonic' refers to speeds that are much higher than the speed of sound.
In the context of running a race, it is typically more desirable for a runner to have a speed that is in a high percentile. A high percentile means that the person is faster than most others. For example, being in the 90th percentile means that a runner is faster than 90% of the other runners.
Interpreting the 40th percentile of speeds in a race, if the 40th percentile is at 7.5 miles per hour, it would mean that 40% of the runners are running at or below this speed, and 60% are running faster.