There is a large number of cubes in a bag. Jason wants to work out an estimate for the number of cubes in the bag.
He takes at random 10 cubes from the bag.
He puts a mark on each cube and then puts each cube back in the bag.
Jason shakes the bag and then takes at random 20 of the cubes.
There is a mark on 3 of the cubes.
Work out an estimate for the total number of cubes in the bag