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

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Answer 1 · 2016-11-16T04:01:31

There were 110 possible points.

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.

$.90x = 99$

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

$x=110$