分数(ぶんすう)

Etymology

• 分子(ぶんし) - numerator (top number)
• 分母(ぶんぼ) - denominator (bottom number)

Types

• 真分数(しんぶんすう) - proper fraction (numerator < denominator)
• 仮分数(かぶんすう) - improper fraction (numerator ≥ denominator)
• 帯分数(たいぶんすう) - mixed number

Operations

• 通分(つうぶん) - finding common denominator
• 約分(やくぶん) - reducing/simplifying fractions

Related math terms

• 整数(せいすう) - integer
• 小数(しょうすう) - decimal
• 百分率(ひゃくぶんりつ) - percentage

How fractions are read

Japanese names the denominator first: 1/2 is 二分(にぶん)の一(いち) (literally 'one of two parts'), and 3/4 is 四分(よんぶん)の三(さん). This is the reverse of the English order, and it is the single most common stumbling block for learners meeting the word.