document.write( "Question 1195486: If the mean of the following numbers is 17, find the c value. Produce an algebraic solution. Guess and check is unacceptable.
\n" ); document.write( "12, 18, 21, c, 13 \n" ); document.write( "

Algebra.Com's Answer #827985 by greenestamps(13200) $\"\"$ $\"About$

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\n" ); document.write( "A typical algebraic solution....

\n" ); document.write( "(12+18+21+c+13)/5 = 17
\n" ); document.write( "12+18+21+c+13 = 85
\n" ); document.write( "64+c = 85
\n" ); document.write( "c = 21

\n" ); document.write( "That method for solving the problem is fine since the numbers are small, so adding the numbers is an easy task.

\n" ); document.write( "If the numbers are much larger but still close together, an often useful method for solving a problem like this is to compare each number to the desired mean, knowing that the \"overs\" and \"unders\" have to balance.

\n" ); document.write( "For this example, with the average being 17....
\n" ); document.write( "12: 5 under
\n" ); document.write( "18: 1 over
\n" ); document.write( "21: 4 over
\n" ); document.write( "13: 4 under

\n" ); document.write( "Note the first three numbers balance; overall the four scores are 4 under the desired average.

\n" ); document.write( "That means c must be 4 over the desired average. So

\n" ); document.write( "ANSWER: c = 17+4 = 21

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