# mid level math question about %.

$A = 1000, B = 1.2$

$A\times B = C (1000\times 1.2 = 1200)$

$X\times C = A (? \times 1200 = 1000)$

Need to find $X$ every time I change $A$ or $B$. Probably there is formula that is able to solve this since the only way I know how to do it is hilariously ignorant and slow.

How do i ask a calculator to do that (: ? Preferably one with syntax I can use with Excel or google.

Use algebra: $X=A/C = A/(A \cdot B) = 1/B$.

• Yeah, thank you for that, I'd almost be embarrassed to ask, except math was never my vocation, life just tends to amuse it self by giving me odd math obstacles here and there. – helena4 Jun 30 '14 at 9:01

If $$x\cdot c = a,$$ then $$x = \frac{a}{c}.$$