Question 215557
After taking 4 quizzes, your average is 76 out of 100. What must your average score be on the next five quizzes to increase your average to 81?


Step 1.  Let x be the average of the next five quizzes.


Step 2.  Let 4*76 be the 4 quizzes with each quiz having a score of 76 so the average of the four quizzes is 76.


Step 3.  There will be a total of 9 quizzes.


Step 4.  The average of nine quizzes is {{{81=(4*76+5x)/9}}}.  Solve for x as follow


Multiply 9 to both sides of equation to get rid of denominator


{{{81=(4*76+5x)/9}}}


{{{9*81=9*(304+5x)/9}}}


{{{729=304+5x}}}


Subtract 304 to both sides of equation to get 5x on the right side


{{{729-304=304+5x-304}}}


{{{425=5x}}}


Divide by 5 to both sides of equation to solve for x


{{{425/5=5x/5}}}


{{{x=85}}}


Step 5.  ANSWER:  To get an overall average of 81, the next five quizzes must average 85.


I hope the above steps were helpful.


For FREE Step-By-Step videos in Introduction to Algebra, please visit http://www.FreedomUniversity.TV/courses/IntroAlgebra and for Trigonometry visit http://www.FreedomUniversity.TV/courses/Trigonometry.


Good luck in your studies!


Respectfully,
Dr J