19. If R1 = 9 ?, R2 = 4 ?, R3 = 2 ?, and R4 = 2 ?, the equivalent resistance Req (in ohms) at terminals a and b is
1. 5
2. 11
3. 19
4. 4
5. 2
20. If R1 = 40 ?, R2 = 10 ?, and R3 = 50 ?, the equivalent resistance Req (in ohms) at terminals a and b is
1. 10
2. 100
3. 2400
4. 48.33
5. 24