Question 513918
First, let's find the sum of your four quizzes (a+b+c+d):
{{{(a+b+c+d)/4 = 82}}} The average of the first four quizzes is 82.
{{{a+b+c+d = 328}}} Now let's call the score on your fifth quiz, x, so...
{{{(328+x)/5 = 85}}} Multiply by 5.
{{{328+x = 425}}} Subtract 328.
{{{x = 97}}}
You will need to get 97 on your next quiz to attain an overall average of 85.