The question also states that Lucy has a winning probability of 1/50, which means that she has 1 chance of winning if the total runners were 50. Therefore, there are 49 runners who may be faster than her.
The fact that Lucy is the 50th slowest runner, means that starting from the slowest she is in 50th position, therefore there are 49 runners that are slower than her.
The total number of runners will be the sum of those faster than Lucy, those slower than Lucy and Lucy: 49 + 49 + 1 = 99
