The remaining rice is: 50-20=30 (kg)
The rice eaten the next day is 2/5 of the remaining rice, which is 30×(2/5)= 12 (kg).
What I ate on the third day was: 30- 12= 18 (kg).
The percentage of rice eaten on the first day is: (20-12) ÷12×100% = 66.7% (approximately equal).
The percentage of rice eaten on the third day is (20-18) ÷ 20×100% =10%.