addition
arithmetic

base
binary

casting out nines
common fraction
cryptarithm

decimal fraction
denominator
division

fly-between-trains problem
four fours problem
fundamental theorem of arithmetic

lowest common multiple

modular arithmetic
multiplication

negative base
number system

percentage
period, of a decimal expansion
place-value system
product
proportional

quotient

ratio
reciprocal
Russian multiplication

St. Ives problem
subtraction

wheat and chessboard problem