Jonah drove the first half of a 100-mile trip in x hours and the second half in y hours.

Which of the following is equal to Jonah's average speed, in miles per hour, for the entire trip?

~$50 \over x+y$~

~$100 \over x+y$~

~$25 \over x$~+~$25 \over y$~

~$50 \over x$~+~$50 \over y$~

~$100 \over x$~+~$100 \over y$~