God this is an ugly language

The code comment clearly says:

;Be sure to return longs. We don't want to return Clojure Ratios!

Probably tests are poorly written as you said. You can simply use a float for the dividend to get a decimal number instead of a ratio.

(/ 5.0 2)
=> 2.5

I propose the solution

(float 5/2)
=> 2.5

Right, the test doesn't match the problem, which means this entire kata is really poorly written or I'm still missing something.

Looks like the tests don't cover that.

How is this correct? It returns Ratios.

(find-average [1 2 3 4])
5/2