In Farmer Donald's hay loft there are a number of ants, mice and chickens. There are ten times as many ants as there are mice and there are four times as many mice are there are chickens. Altogether there are 1806 feet. How many chickens are there?
There are 7 chickens, 28 mice and 280 ants. For every chicken (2 legs) we have 4 mice (16 legs) and 40 ants (240 legs) = 258 legs. So we can divide the total number of legs by 258, giving 1806 ÷ 258 = 7 (chickens). QED.