sebuah trafo memiliki efesiensi 75% tegangan inputnya 220v dan tegangan output nya 110v jika kuat arus primer yang mengalir 2A kuat arus sekundernya adalah

A transformer has 75% efficiency:
η = 75% => [tex] \frac{75}{100} [/tex]

Its voltage input is 220v:
Vp = 220

Its voltage output is 110v:
Vs = 110

The transformer has 2A current on its input:
Ip = 2

Asked: The current output.

Formula:
η=[tex] \frac{Vs}{Vp} [/tex]×[tex] \frac{Is}{Ip} [/tex]×100%

Put them together:
[tex] \frac{75}{100} =[/tex][tex] \frac{110}{220}[/tex]×[tex] \frac{Is}{2} [/tex]×100%

Calculate:
[tex] \frac{75}{100} [/tex] = [tex] \frac{110.Is}{440} [/tex]×100%
[tex]110Is[/tex]×[tex]75[/tex]=[tex]440[/tex]×[tex]100[/tex]×1
[tex]8250Is = 33000[/tex]

Divide both sides by 8250:
[tex] \frac{8250Is}{8250} = \frac{33000}{8250} [/tex]

Result:
[tex]Is = 4[/tex]

Conclusion:
The output current of the transformer is 4A