Explanation:
18 minutes in total.
4 1/2 minutes per pot.
so, all we need to do is find out how often 4 1/2 fits into 18. that is what division is for.
18 / (4 1/2)
4 1/2 = 2×4/2 + 1/2 = 8/2 + 1/2 = 9/2
18 / 9/2 = 18/1 / 9/2 = 2×18 / 9×1 = 36/9 = 4
there are 4 coffee pots.