In other words, from ten jin of soybeans, Grandpa Wang's family could make at least thirty jin of tofu.
With the prices at that time, one jin of soybeans was two copper coins, ten jin was twenty cents, and twenty cents divided by thirty jin meant that the cost for each jin of tofu was merely 0.6 copper coins. Adding brine and other miscellaneous items, the cost could be rounded up to just over one copper coin per jin.
However, making tofu also involved daily losses, labor, transportation costs, and so on, so one could not simply assume the cost was one copper coin. It would have to be calculated up to two copper coins.
