document.write( "Question 620819: Johnny was ill and had to take a test a day late. His 99 raised the class average from 71 to 75. How many students, including Johnny, took the test?\r
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Algebra.Com's Answer #390415 by htmentor(1343)\"\" \"About 
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Johnny was ill and had to take a test a day late. His 99 raised the class average from 71 to 75. How many students, including Johnny, took the test?
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\n" ); document.write( "The average score is determined by:
\n" ); document.write( "average = S/n, where S = the sum of scores and n is the number of students
\n" ); document.write( "Let S = the sum of scores before Johnny took the test
\n" ); document.write( "Let n = the total number who took the test
\n" ); document.write( "Then the original class average = 71 = S/(n-1)
\n" ); document.write( "The adjusted average with Johnny's score included = 75 = (S+99)/n
\n" ); document.write( "We have two equations and two unknowns
\n" ); document.write( "Cross-multiplying gives
\n" ); document.write( "71(n-1) = S [1]
\n" ); document.write( "75n = S + 99 [2]
\n" ); document.write( "Subtract [1] from [2]:
\n" ); document.write( "4n + 71 = 99
\n" ); document.write( "4n = 28
\n" ); document.write( "n = 7
\n" ); document.write( "So 7 students took the test\r
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