Question

efficiency is the ratio of work input to work output. it is expressed as a percentage (%).
the higher the percentage (%) is, the higher the efficiency of the machine.
work input is the amount of work put into a machine.
work output is the amount of work done by the machine.
friction is the opposing force one object exerts on another when they touch.
an ideal machine is 100% efficient and it loses no work due to friction. ideal machines do not exist.
what is the efficiency of an ideal machine?
a machine with 150% efficiency
a machine with 100% efficiency
a machine with 50% efficiency

Explanation:

The problem is about the concept of machine efficiency. An ideal machine has no work loss due to friction, so its efficiency is 100%. A machine with 150% efficiency is impossible as work output can't exceed work input. A 50% - efficient machine has significant work loss.

Answer:

B. A machine with 100% efficiency