Question

a tank 4/5 full needs 75 litres to fill it up.how many litres does it hold when full

Answer 1

x - the volume of the tank

$\frac{4}{5}x+75=x \\ 75=x-\frac{4}{5}x \\ 75=\frac{1}{5}x \ \ \ |\times 5 \\ x=375$

The tank holds 375 liters when full.