There is 5/6 of an apple pie left from dinner. tomorrow, victor plans to eat 1/6 of the pie that was left. how much of the whole pie will he eat tomorrow?

5/6 = 83% 
1/6= 16%

83% of the apple pie was left from dinner. 
Victor is gonna eat 16% of the pie tomorrow 
You have to subtract 16% from 83%
In other words 5/6-1/6

The denominators are same so you don't have to do anything to them  
5/6 - 1/6 

5-1=4

4/6 of the pie would be left 
In simplest form it would be 

4/6      ÷2
=2/3

2/3 is in simplest form 

-- 5/6 of a pie is left from dinner.

-- Victor will eat 1/6 of THAT tomorrow,
    so he will eat (1/6 of 5/6 of a pie).

-- (1/6) x (5/6) = 5/36 of a pie, or about 13.89% of a whole pie.