Trig help!!

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mathie

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Jun 29, 2011
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The number of minutes students took to complete a quiz is summarized in the table below.

Minutes: 14 15 16 17 18 19 20
# of Students: 5 3 x 5 2 10 1


If the mean number of minutes was 17, which equation could be used to calculate the value of x?

1.) 17 = 119 + x divided by x

2.) 17 = 119 + 16x divided by x

3.) 17 = 446 + x divided by 26 + x

4.) 17 = 446 + 16x divided by 26 + x
 
mathie said:
The number of minutes students took to complete a quiz is summarized in the table below.

Minutes: 14 15 16 17 18 19 20
# of Students: 5 3 x 5 2 10 1


If the mean number of minutes was 17, which equation could be used to calculate the value of x?

1.) 17 = 119 + x divided by x

2.) 17 = 119 + 16x divided by x

3.) 17 = 446 + x divided by 26 + x

4.) 17 = 446 + 16x divided by 26 + x
Click to expand...

First calculate the total number of students.

Then think about the definition of average (mean).

Please share your work with us indicating exactly where you are stuck - so that we may know where to begin to help you.
 
Total number of students = 26 + x, but I don't know where the number "446" comes from?
 


Subhotosh suggested that you consider the process of how we average a list of numbers. You've averaged numbers before, yes?

In case you forgot, the average of a set of numbers is their total divided by the number of numbers in the set.

I'll use the following modified data, as an example. Let's find the average number of minutes that it took the following 15 students to complete the quiz.

Code: 
      Minutes:   14   15   17   18

# of Students:    5    3    5    2

From this data, we see the list of numbers to average is:

14, 14, 14, 14, 14, 15, 15, 15, 17, 17, 17, 17, 17, 18, 18

What is their sum?

How many numbers are there in this set?

The average of these numbers is their total divided by their count:

(5)(14)+(3)(15)+(5)(17)+(2)(18)5+3+5+2=15.7\displaystyle \frac{(5)(14) + (3)(15) + (5)(17) + (2)(18)}{5 + 3 + 5 + 2} = 15.7

It took an average of 15.7 minutes to complete this quiz.


How would we have set up the average calculation, if one of those student numbers in the chart were unknown?

 
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