Question

21 is 72% of which number

Answer 1

is actually "x", which oddly enough is the 100%.

we also know that 72% of "x" is 21, hmmm what the heck is "x"?

`\begin{array}{ccll} amount&\%\\ \cline{1-2} x & 100\\ 21& 72 \end{array} \implies \cfrac{x}{21}~~=~~\cfrac{100}{72} \implies\cfrac{ x }{ 21 } ~~=~~ \cfrac{ 25 }{ 18 } \implies 18x=(21)(25) \\\\\\ x=\cfrac{(21)(25)}{18}\implies x=\cfrac{175}{6}\implies x=29(1)/(6)\implies x=29.1\overline{666}`

Answer 2

29.12

Explanation:

You would need to set up a proportion to do this...