Jean Luc was asked to record the times of 20 athletes in a long distance race. He started his stopwatch when the race began and then went to sit in the shade, where he fell asleep. On waking, he found that x athletes had already completed the race but he was able to record the times taken by all the others. State the possible value(s) of x if Jean Luc was able to use his data to calculate:

a. The variance of the times taken by the 20 athletes.

b. The interquartile range of the times taken by the 20 athletes.