Answer: 40 percent
Step-by-step explanation: real value = 1.5 liters ,estimated value = 2.1 liters.
Percentage student's estimate = (difference in estimate/ real value) × 100
Difference in estimate = 2.1-1.5 = 0.6
Real value = 1.5
Percentage student's estimate = (0.6/1.5)×100 = 0.4×100 = 40 percent