There are two similar problems in this book. The first one begins like this (my translation):
Una piscina tiene el doble de largo que de ancho. / A swimming pool has its length equal to twice its width.
The second one says:
Una parcela mide el triple de larga que de ancha. / A plot of land measures three times as long as it is wide.
My question is why did largo and ancho change to the feminine versions in the second sentence? Both the subjects are feminine. The verb changed from tener to medir, but what difference does that make'