[tex]15 \times 250 \ ml=3750 \ ml[/tex]
Fifteen 250 ml glasses contain 3750 ml of the drink, and 750 ml of orange squash.
[tex]3750 \ ml - 750 \ ml=3000 \ ml[/tex]
There are 3000 ml of water in 3750 ml of the drink.
3000 ml of water - 3750 ml of the drink
x l of water - 10 l of the drink
[tex]\frac{3000 \ ml}{3750 \ ml}=\frac{x \ l}{10 \ l} \\
3750x=10 \times 3000 \\
3750x=30 000 \\
x=8[/tex]
8 litres of water are needed to make 10 litres of this drink.