40×

40× is a notation that uses the multiplication symbol × to indicate a factor of forty. It is read as “forty times” or “forty-fold” and is used to describe a relationship between a quantity and a reference amount.

In mathematics, 40×a means forty multiplied by a. In science and engineering, the same notation appears in various contexts such as magnification (a 40× lens), dilution (a 40× dilution), and fold-change (a 40× increase or decrease). The concept is to express how many units of one quantity correspond to a single unit of another.

The symbol × is the standard multiplication sign in many notations; in plain ASCII, 40× is sometimes written as 40x or 40*. These alternatives are common in informal contexts or computer code, but the formal symbol × is preferred in typographic text. The essential idea is that 40× denotes a multiplicative factor, not an addition.

Examples include: 40×2 = 80; a 40× magnification lens enlarges an object forty times; a 40× dilution reduces the concentration by a factor of forty, yielding a forty-fold dilution.

See also: Multiplication, Magnification, Fold change, Scale.