A cubical water tank has an internal edge of 1.2 m. How many litres does it hold when full?

Volume = $1.2^3=1.728{\text{m}}^3$. Since $1{\text{m}}^3=1000$ litres, the tank holds $1.728\times 1000=1728$ litres. (1.728 leaves the answer in $m^3$; 172.8 multiplies by 100 and 17280 by 10000 — the factor from $m^3$ to litres is exactly 1000.)