A correct multiplicative answer is relatively rare. By far the most common answer is something like: “2 units because the water level on the right side increased by two units so the water level on the left side must decrease by two units and 4 – 2 = 2.” Less frequently the reason for two units is: “Before there is a total of 10 units because 4 + 6 = 10. The total number of units must stay the same so the answer is 2 because 2 + 8 = 10.”