2. Error reason: False score refers to a score greater than or equal to 1, and the reciprocal of 1 is still 1, so the reciprocal of false score may be equal to 1.

3. Correct reason: 3× 1/5 = 3/5 (ton), 1× 3/5 = 3/5 (ton).

4. Brother Monkey is right. Reason: Bajie ate a third of the whole watermelon, and Monkey ate (1- a third) × half = a third.