SOLUTION: Sally's quiz average in a class is exactly 84. After 5 consecutive scores of 100, her quiz average goes up to exactly 92. How many quiz scores does Sally have after the 5 consecuti

Algebra ->  Average -> SOLUTION: Sally's quiz average in a class is exactly 84. After 5 consecutive scores of 100, her quiz average goes up to exactly 92. How many quiz scores does Sally have after the 5 consecuti      Log On


   

Question 929457: Sally's quiz average in a class is exactly 84. After 5 consecutive scores of 100, her quiz average goes up to exactly 92. How many quiz scores does Sally have after the 5 consecutive 100s?
Answer by richard1234(7193) About Me  (Show Source):
You can put this solution on YOUR website!
Assuming the quizzes are equally weighted:

Let s = # quiz scores before the 5 scores of 100. Then 84s = sum of the scores, and 84s + 5*100 = 84s + 500 = the sum of her scores afterwards.

She now has s+5 quiz scores, so (84s + 500)/(s+5) = 92. Solving, s = 5.

Another way to see that she had 5 scores beforehand is to note that 92 is exactly halfway between 84 and 100.