Posted by **liz** on Tuesday, February 28, 2012 at 8:55pm.

A prof. teaches 2 calc. classes. The first class has 25 students and their mean on the 1st test was an 82. The 2nd class has 15 students and their mean on the same test was a 74. What is the mean on this test if the prof. combines the score for both classes?

Is the answer the mean cannot be calculated since the individual scores of each student are not available.

- Math for the middle school and elementary teacher -
**MathMate**, Tuesday, February 28, 2012 at 9:38pm
To calculate the mean, you need the *total* score and the *total* number of students.

Can you find a way to reconstitute these two numbers, knowing that

mean = total score / number of students

- Math for the middle school and elementary teacher -
**liz**, Tuesday, February 28, 2012 at 9:42pm
I don't think you can find the total score because you would need the individual scores, right? I tried dividing 82/25 but that wouldn't work because we don't have all the scores...am I on the right track if not, can i please have some guidance? thank you!

- Math for the middle school and elementary teacher -
**MathMate**, Tuesday, February 28, 2012 at 10:03pm
hint:

For each class

mean = total score / number of students

=>

for each class

total score=mean*number of students

So the total score for each class is known. Can you find the total score for both classes? Total number of students?

- Math for the middle school and elementary teacher -
**liz**, Tuesday, February 28, 2012 at 10:19pm
The answer is 79, correct? Thank you for your guidance and help:)

- Math for the middle school and elementary teacher -
**MathMate**, Tuesday, February 28, 2012 at 11:08pm
Excellent & well done!! :)

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