Accuracy of the result question short? We have 1/(4,5) .
When we do the divison,what accuracy does the result have?

I assume you're talking about significance arithmetic.  When dividing numbers, "the result is rounded to the number of significant figures in the [operand] with the least significant figures."  Assuming that your dividend really is $1$ (and not, say, $1.0$), then your quotient should be rounded to one significant figure.  That is, $1/4.5\approx 0$.  But if your dividend is, say, $1.0$, then  your quotient should be rounded to two significant figures.  That is, $1/4.5\approx 0.2$.
