How to find average

Question

``Danielle's test scores are 86,80,84, and 90. The final exam will count as two-thirds of the final grade. What score does Danielle need on the final in order to earn a B, which requires an average score of 80? What score does she need to earn an A, which requires an everage of 90?''.

Answer 1

Her current grade is (86+80+84+90)/4 = 85.  This represents 1/3 of her grade.  

 

2x/3 + (1/3)85 = 90.

2x/3 + 85/3 = 90

2x + 85 = 270

2x = 185

x = 92.5