The question is:

Ice skaters, ballet dancers, and basketball players executing vertical leaps often give the illusion of "hanging" almost motionless near the top of the leap. To see why this is, consider a leap that takes an athlete up a vertical distance h. Of the total time spent in the air, what fraction is spent in the upper half (i.e. at y>1/2)?

The answer is 70.7% but I don't know how to get that. Thanks to anybody who can help :)

Can you work out the total time for a 10m high jump?
How about the total time for a 20m high jump?

The 10m high jump is identical to the top half of the 20m high jump, so you can directly compare these two results.

Let me know if you need further help.