Question

jacob used 1/7 of liter of water to fill 1/9 of the fish aquarium. how many liters of water are needed to fill the aquarium

Answer 1

To find the result we can use proportion

$\frac{1}{7} --------------- \frac{1}{9} \\ x ---------------1$

Now we have crossmultiply, so
$\frac{1}{7}*1= \frac{1}{9} *x$      /*9     (multiply both sides by 9)
$\frac{9}{7}=x$ - its the result