A juice seller can pour his entire stock exactly into bottles of 750 mL, or exactly into bottles of 900 mL, or exactly into bottles of 1250 mL, with nothing left over each time.
What is the least amount of juice he can have (in litres)?

The stock must be a common multiple of 750, 900 and 1250 mL, so the least is their LCM. $750=2\times 3\times 5^3,900=2^2\times 3^2\times 5^2$ and $1250=2\times 5^4$, so LCM = $2^2\times 3^2\times 5^4=22500$ mL = 22.5 litres (that is 30, 25 and 18 bottles respectively). Answering 0.05 L uses the HCF, 50 mL, instead of the LCM; 45 L is twice the LCM; 2.25 L slips a decimal place.