Donnovan earned 99 points on his science project. If his grade was a 90%, how many points were possible?

1 Answer
Nov 16, 2016

Answer:

There were 110 possible points.

Explanation:

This problem could be rephrased as "99 is 90% of what number?".

One way to set it up is to use "is over of equals percent over 100".

# "is"/"of" = "%"/ 100#

#99/x = 90/100#

Cross multiply.

#90x = 99(100)#

#90x=9900#

#(90x)/90 = 9900/90color(white)(aaa)#

#x=110#

A second way to think about the problem is "90% of x is 99#.
"Of" indicates multiplication and "is" means equal.

Convert 90% to the decimal .90 by dividing 90 by 100.

#.90x = 99#

#(.90x)/.90 =99/.90#

#x=110#