Answer :
Explanation:
If the fourth pupil has a mass of x, and the fifth pupil has a mass of x+5, then the mean mass is:
51 = (49 + 53 + 52 + x + x+5) / 5
255 = 159 + 2x
x = 48
x + 5 = 53
The fourth pupil has a mass of 48 kg.
The fifth pupil has a mass of 53 kg.