document.write( "Question 1094468: Seth scored an 82%, 88%, and 75% on three tests. What score must he get on the fourth test to bring his average to 80%? \n" ); document.write( "

Algebra.Com's Answer #709099 by greenestamps(13200) $\"\"$ $\"About$

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To have an average of 80 on 4 tests, the total of the 4 scores must be 4*80 = 320.
\n" ); document.write( "The sum of the three tests he already took is 82+88+75 = 245.
\n" ); document.write( "The score he needs on the 4th test is 320-245 = 75.

\n" ); document.write( "Or when the numbers being averaged are all close together, as they are in this case, you can solve the problem like this:
\n" ); document.write( "1st test: 2 points over the desired average (82-80 = +2)
\n" ); document.write( "2nd test: 8 points over the desired average (88-80 = +8)
\n" ); document.write( "3rd test: 5 points below the desired average (75-80 = -5)

\n" ); document.write( "Cumulatively for the first three tests he is 5 points over the desired average: (+2)+(+8)+(-5) = +5

\n" ); document.write( "So on the 4th test, if he wants an average of exactly 80, he has to get a score that is 5 points below that average -- to \"balance out\" the \"extra\" 5 points he has going into the 4th test.

\n" ); document.write( "And 5 points below 80 is 75.

\n" ); document.write( "So again by this method he needs 75 on the 4th test to get an overall average of 80.

\n" ); document.write( "With all the word of explanation, it sounds like a lot of work. But the calculations are easier and faster then the first method. Really all you do with this alternate method is this:

\n" ); document.write( " $\"%28%2B2%29%2B%28%2B8%29%2B%28-5%29+=+%2B5\"$ --> the next score should be -5 \n" ); document.write( "

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