Suppose the producer supplies 50 units at Rs.X.
Given, P=Rs.20;P1=Rs.X;△P=Rs.(X−20)
Q=100 units;Q1=50 units;△Q=Q1−Q=(50−100)units=(−)50 units
ES=2
Price elasticity of supply (ES)=PQ×△Q△P
2=20100×−50X−20
⇒2=−10X−20
⇒X−20=−102
⇒X−20=−5
⇒X=−5+20=15
The producer will supply 50 units at Rs.15.