Solution :
We know, by to Ohm's law :
[tex]Current = \dfrac{Voltage}{Resistance}[/tex]
For, case 1 :
[tex]I = \dfrac{5}{20}\ A = 0.25 \ A[/tex]
For, case 2 :
[tex]I = \dfrac{20}{20} \ A\\\\I = 1 \ A[/tex]
For, case 3 :
[tex]I = \dfrac{50}{20}\ A\\\\I = 2.5 \ A[/tex]
Therefore, this is the required solution.