A simple machine has efficiency 90%. What does it mean? No machine has 109 efficiency, why?​

Efficiency of a machine is 90% this means that the total energy produced to the machine only 90% is useful and given as a output.

Machines are not 100% efficient because some of the work done by a machine is used to overcome friction

Explanation:

A simple machine has efficiency 90% means that 10% of the applied effort is wasted due to overcoming friction and 90% of the applied force is used in doing useful work .No machinr has hundred percent efficiency because every machine is affected by overcoming friction .

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)