document.write( "Question 356737: Kate took a math test that she missed due to sickness. Her perfect score of 100 points raises class average from 80 points to 81. How many students including her in the class took the test? \n" ); document.write( "

Algebra.Com's Answer #254660 by robertb(5830) $\"\"$ $\"About$

You can put this solution on YOUR website!
Let x = #students who took the test. Then the sum of all scores in the test without her score is 80x. Plus her score, the total sum would be 80x + 100.
\n" ); document.write( "Dividing by x+1 (as there would be x +1 students now),
\n" ); document.write( " $\"%2880x+%2B+100%29%2F%28x%2B1%29+=+81\"$ .
\n" ); document.write( " $\"80x+%2B+100+=+81x%2B81\"$ , after cross-multiplication.
\n" ); document.write( " $\"100-81+=+81x-80x\"$ ,
\n" ); document.write( " $\"x+=+19\"$ , the number of students who took the test. \n" ); document.write( "

\n" );