Chiu Chang Suann Jing/Examples/Example 1

Example of Problem from
Two and a half piculs of rice are bought for $\dfrac 3 7$ of a tael of silver.

How many piculs of rice can be bought for $9$ taels?

Answer
Let $x$ be the required quantity.


 * $\dfrac x 9$ piculs can be bought with $1$ tael.

Hence $\dfrac x 9 \times \dfrac 3 7$ can be bought for $\dfrac 3 7$ of a tael.

That is:
 * $\dfrac x 9 \times \dfrac 3 7 = \dfrac 5 2$

and so:
 * $x = 9 \times \dfrac 5 2 / \dfrac 3 7 = 52 \frac 1 2$

One picul, apparently, is equal to about $65$ kilograms.