等分 and 均等: equal parts and an even distribution
Compare dividing a cord into four equal parts with force distributed evenly, keeping the part count separate from each part’s size.
Dividing into equal parts
等分, read とうぶん, means division into equal parts. 長いひもに印を付けて四等分する。 describes marking a long cord and dividing it into four equal parts.
四等分 specifies four parts of equal length. It does not specify four centimeters per part; the total length is needed.
Even allocation or distribution
均等, read きんとう, describes an even allocation or distribution. 板に力が均等にかかるよう支えを置く。 describes placing supports so that force acts evenly on a board.
It does not instruct cutting the board into equal pieces. 均等 can describe a force distribution as well as an allocation of objects.
The whole and each part
八十センチのひもを四等分しました。 reports dividing an eighty-centimeter cord into four equal parts. Each is twenty centimeters; distinguish count from length.
四つに分けました。 alone does not establish equal lengths. Check whether equal division was specified.
What is the length of each part when an eighty-centimeter cord is 四等分?
Show the answer and why
Twenty centimeters. Four equal parts give eighty divided by four.