Nine Chapters on Mathematical Art, Vol. 1

Now there is a winnowing-basket shaped field ji tian, with a tongue width of 20 bu, a heel width of 5 bu, and 50 bu in length.
Ask: What is the area of the field?

There is another winnowing-basket field, with a tongue width of 117 bu, a heel width of 50 bu, and 135 bu in length.
Ask: What is the area of the field?

Procedure: Combine the heel and tongue widths and halve them, then multiply by the length. Divide by the mu-method.
Dividing the winnowing-basket field in the middle results in two trapezoidal fields, so the method is similar. One can also combine the heel and tongue widths, halve the length, and multiply them.

Now there is a circular field with a circumference of 30 bu and a diameter of 10 bu. We, Chunfeng and others, respectfully note: The intention of the method is to use 3 for circumference and 1 for diameter.