A cuboidal tank measures 2 m by 1.5 m by 1 m inside. It is filled to the brim using a bucket that holds 15 litres. How many bucketfuls are needed?

Capacity = $2\times 1.5\times 1=3{\text{m}}^3=3000$ litres, so the number of bucketfuls = 3000/15 = 200. (Taking $1{\text{m}}^3$ as 100 litres gives 20 and as 10000 litres gives 2000; dividing the bare $3{\text{m}}^3$ by 15 gives 0.2, which compares a volume in $m^3$ with one in litres.)