mid level math question about %.

Question

$A = 1000, B = 1.2$

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

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

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.

Thx in advance.

Answer 1

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

Answer 2

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