Strange behavior of PHP time math: Why is strtotime() returning negative numbers?

Question

I\'m trying to do some very basic time math - basically, given inputs of time and distance, calculate the speed. I chose to use strtotime() to convert the time inputs into s

Answer 1

If you want to do something like that, I think you want to just do some math on the time strings themselves and convert them to a number of seconds, like this: