we know all three weight 1/5 of a ton, how much is it for one?
well, since there are 3 of them, one is just 1/3 of the whole 1/5 of a ton, how much is 1/3 of 1/5? well, is just its product,
[tex]\bf \cfrac{1}{3}\cdot \cfrac{1}{5}\implies \cfrac{1}{15}\textit{ of a ton}[/tex]
