Percentage is the same as a fraction over 100, where the number 100 represents a 'whole'.
Therefore, if 65% are male, it means if there were 100 runners in total, 65 of them would be male, so your fraction would be 65/100.
However, you can simplify this fraction as both 65 and 100 have common factors. So you keep dividing both numbers by its factors until there are no more common factors left. This will leave you with 13/20.
Therefore your final answer is 13/20.