I think we can verify results on some kind of problem.
Let's say we have n number of items and need to sort it. We'll give it to worker-1, worker-1 will give us the result. We can verify it O(n) time. Please consider that it take at least O(n*log(n)) time to produce the result. Additionally we should consider how large is n items? (concern about network speed)
Another example, f(x)=12345, and function is given. Purpose is to find value of x. We can test it by replace x with some worker's result. I think some problems that are not verifiable are difficult to give to someone.
