DAY 81

Comment

One approach is to consider a similar but extreme version of the problem (assuming that this is a valid thing to do ...).
Imagine, for example, that Hanif cycles at 19 mph on the outward leg (ie 10 mph + 9 mph) and at 1 mph on the return (10 mph - 9 mph), while Jenny still cycles at 10 mph both ways.
Then Hanif is going to take a considerable time on the return leg. (If you are not convinced, consider 19.9 mph and 0.1 mph, say.)
Alternatively: At first sight it seems that Hanif's average speed is the same as Jenny's;
but this is only true if he travels at 15 mph and at 5 mph for the same length of time.
Is this the case?

Answer

Jenny wins.

Readers' methods

Kirsty Lauder, Peebles:
Imagine the tree is 15 miles away.
Then Hanif will take 1 hour + 3 hours, and
Jenny will take 1.5 hours + 1.5 hours.

xxx