Why is "quintal" 100 pounds?

Solution 1:

Quintal does not derive from Middle French quint from Latin quintus, but from Latin centenarius "containing a hundred". Its origin is quite convoluted as shown below:

• Quintal became Late Latin centenarium pondus, then in succession, Late Greek, κεντηνάριον (kentenarion), Arabic, qintar. The qintar was reimported to Europe by traders during the Middle Ages, where it became Mediæval Latin quintale, and finally Old French quintal before passing into the English language from French.

• Languages drawing its cognate name for the weight from Arabic qintar include Spanish quintal, French quintal, Italian quintale, Portuguese quintal, Ukrainian квінтал (kvintal), Esperanto kvintalo. Languages taking their cognates from Germanicized centner include German Zentner, Lithuanian centneris, Swedish centner, Polish cetnar, Russian центнер (tsentner), Estonian tsentner, and Spanish centena.

• Many European languages have come to translate both the Imperial and US hundredweight as their cognate form of quintal or centner.

From: (www.liquisearch.com)