The increase in volume will be minimum when a, b and c are 10% each. The new volume will be 1.1×1.1×1.1=1.331 times of the old volume. So the percentage increase in volume will be 33.1%. Similarly, the increase in volume will be maximum when a, b and c are 20% each. The new volume will be 1.2×1.2×1.2=1.728 times of the old volume. So the percentage increase in volume will be 72.8%. As the final percentage increase in volume is an integer, the value must be an integer from 34 to 72 i.e. 39 distinct values are possible.