I am just doing some reading on power electronics and I came across this question. They state the answer, which is 0.55. What I can't figure out is how they got the answer. The questions is:

*"A dc-dc converter has an input voltage of Vg=5V, and it supplies a computer processor with V=0.5V at 50A (25 W). The converter is a buck converter, and it uses a diode having a forward voltage drop of 0.5V. All losses other than the diode conduction loss are negligible. Estimate the efficiency of this converter"*

Efficiency is given by PowerOut/PowerIn. The Power out is 25W, information is given. I apologize if this seems vague but this is essentially all the information I have. I am assuming the Diode is acting like a parallel switch to the output and a MOSFET in series with the voltage source Vg. If someone can help me understand the process of getting the answer. I did a quick search on here but with no luck. Thank you in advance.