An estimate for (302 x 9.96) / (0.51) would be: (300 x 10 x 2) or 6000. (Dividing by 0.5 is the same as multiplying by 2 because 0.5 = 1/2. Remember that when you divide by a fraction, you flip it upside and multiply).

An estimate for (31 x 4.92)/(0.21) is (30 x 5 x 5) or 750. (Dividing by 0.2 is the same as multiplying by 5, because 0.2 = 1/5)