A district agriculture office argues that its 300-rupee soil test is worth the money to every grower of the tract, since the additional yield the tract's growers obtained after testing, averaged over them, came to far more than 300 rupees a grower. Which of the following is an assumption on which the office's argument depends?

The office moves from an average benefit to a benefit for every grower, and that passage holds only if the benefit is fairly evenly spread. Suppose one grower in twenty had a badly deficient field, gained twenty thousand rupees by correcting it, and the rest gained nothing: the average would still stand far above 300 and nineteen growers in twenty would have wasted their money. The argument therefore assumes the gain is not bunched in that way. Whether the office profits on the fee bears on the office's motive and not on the grower's return. That every grower was tested is neither needed nor claimed, since the office is recommending the test to those who have not had it. And past crop failures describe the tract's fortunes without bearing on how this year's gain was distributed.