Let x equal the amount of time passed. Since the time remaining is
of the time that has passed, this time can be represented as (1/4)x. Converting to decimal form may make this problem easier, so change
()x to
25x . Since 1x is the time passed and
.25x is the time remaining, then
1x+.25x is the total time. This is equal to
1.25x . To calculate the percent of the period that is over, use the proportion
=% Now set up a proportion using the time passed as the part and the total time for the class as the whole.
=Cross-multiply to get
1.25x=100.
Divide both sides by 1.25 .
=x=80%80% of the class period is over.
For this particular question, the number of minutes in the class period is not needed to solve the problem.