The task is to generate the correct answer for a given math problem.
--------
Question: Problem: a father said to his son , ` ` i was as old as you are at the present at the time of your birth ' ' . if the father ' s age is 52 years now , the son ' s age 5 years back was :

Answer: d ) 21


Question: Problem: what is the greatest prime factor of 2 ^ 10 - 1 ?

Answer: 3


Question: Problem: if there are 86 workers in a factory , and on a certain day , 72 were present . calculate the percentage that showed up for work ? ( round to the nearest tenth ) .

Answer:
83.7 %