Just as with "regular" numbers, square roots can be added together. But you might not be able to simplify the addition all the way down to one number. Just as "you can't add apples and oranges", so also you cannot combine "unlike" radical terms. In order to be able to combine radical terms together,
If a runner is behind you, s/he must have taken longer, so the times of all of the runners who finished after you did must be greater than 45.5 minutes