Final answer:
About 22.5 lbs of the student's weight is water.
Step-by-step explanation:
Water makes up about 3/4 of a person's weight. If a student weighs 30 lbs, the amount of water in their weight can be calculated as follows:
Weight of water = 3/4 x weight of student
Weight of water = 3/4 x 30 lbs
Weight of water = 90/4 lbs
Weight of water = 22.5 lbs
Therefore, about 22.5 lbs of the student's weight is water.