If the work put into a lever is 25.0 joules and the work done by the lever is 20.0 joules, what is the efficiency of the lever?

Efficiency of the lever is 80 %.

Explanation:

Given that, if the work put into a lever is 25.0 joules and the work done by the lever is 20.0 joules. We need to find the efficiency of the lever. The mathematical expression for the efficiency is given by :

Where

are output and input work respectively.

So, the efficiency of the lever is 80 %. Hence, this is the required solution.    

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form