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Twelve students were absent this is 1/10 of the class how many students are in the class

This is a fifth grade class

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Kathye P. | Math Geek, passionate about teachingMath Geek, passionate about teaching
5.0 5.0 (150 lesson ratings) (150)

Hi, Wyatt.

You can solve this problem by using a proportion, comparing absent students to total students.

absent       12          1
total           x    =    10       (the equal sign is supposed to be in the middle, but I can't do that here)

In a proportion, the cross products are equal. That is:

12 * 10 = 1 * x

120 = x

There are 120 students in the class.

Kathryn A. | MS in Applied MathematicsMS in Applied Mathematics
5.0 5.0 (2 lesson ratings) (2)

Hi Wyatt, 

Another way to think about this question is to try to turn the sentence into an equation that you can solve.  The number we're looking for is the total number of students in the class, so we'll use "x" for that part.  

12 students (who happened to be absent) is equal to 1/10th of the total number of students.  Whenever a number (lets call it "a") is equal to a fraction (or a percentage) of another number (we'll call this one "b"), we know that "a" is equal to the fraction multiplied by "b". So in this case, 12 is equal to 1/10 multiplied by the total number of students.

So 12 = 1/10 * x, which can also be written 12 = x/10. 

To solve for x, we multiply both sides by 10 and arrive at the answer x = 120.


The way the question is worded is a little ambiguous, but Robert may be right.  The answer is 120 if you are looking for the TOTAL number of students in the class.  The answer is 120 - 12 = 108 if you are looking for the number of students currently present in class.

Robert J. | Certified High School AP Calculus and Physics TeacherCertified High School AP Calculus and Ph...
4.6 4.6 (13 lesson ratings) (13)

Use ratio concept,

# of students absent : # of students present

= 1 : 9

= 12 : 108

Answer: There are 108 students in the class right now.