Going into the final exam which will count as two-thirds of the final grade, Mike has test scores of 86,80,84,and 90. What score does he need on the final to earn an average score of 80?

Question

Is this right:
(86+80+84+90)/4 = 80
2/3x(85)= 80

or ((86+80+84+90+(2/3x))/5 = 80

Answer 1

the mean of the four test scores is worth 1/3 of his grade while his final is worth 2/3 of his grade

here's how to set it up:
(1/3)[(86+80+84+90)/4]+(2/3)x=80