Help with (mean) problem.

• October 20th 2006, 03:50 PM
birdie41
Help with (mean) problem.
I would like to know the process of finding the answer to this problem.

A student has earned scores of 87, 81, and 88 on the first 3 of 4 tests. If the student wants an average (arithmetic mean) of exactly 87, what score must she earn on the fourth test? Thankyou.
• October 20th 2006, 04:43 PM
topsquark
Quote:

Originally Posted by birdie41
I would like to know the process of finding the answer to this problem.

A student has earned scores of 87, 81, and 88 on the first 3 of 4 tests. If the student wants an average (arithmetic mean) of exactly 87, what score must she earn on the fourth test? Thankyou.

Assume the 4th score is x. Then the average of the four scores would be:
$\frac{87+81+88+x}{4} = 87$

$256 + x = 348$

So x = 92.

-Dan
• October 20th 2006, 06:35 PM
birdie41
How did you get 348?
• October 21st 2006, 03:57 AM
topsquark
Quote:

Originally Posted by birdie41
How did you get 348?

Sorry, I should have written that step out. Here's the whole thing:
$\frac{87+81+88+x}{4} = 87$

$\frac{256+x}{4} = 87$

$4 \cdot \frac{256+x}{4} = 4 \cdot 87$

$256 + x = 348$

$256 + x - 256 = 348 - 256$

$x = 92$

-Dan