I am reading the section on counting arithmetic operations in Strang's book. It says:
[The] operations are of two kinds. We divide by the pivot to find out what multiple (say $\ell$) of the pivot is to be subtracted. When we do this subtraction, we continually meet a "multiply-subtract" combination; ...
[In the end he gets the value $\dfrac {n^3-n}{3}$ for the number of operations required to reduce the whole matrix.]
My question is, why we call "multiplication-subtraction" one operation, when it is in fact two. Is it because in general, a "multiplication-subtraction" takes the same ammount of time for a computer to do as a "division"?
Thanks.