Markus scored 85, 92, 82, and 94 on the first four tests of the semester. His teacher had not yet told him his score on his fifth tests. Which equation could Markus use to determine the score of the fifth test, x?

If Markus wants to use his average score to guess what his 5th score would be he would use the equation for mean to find his 5th test score:

(85 + 92 + 82 + 94) / 4 = average

and the average could give Markus a guess at what his 5th test score might be.

Now if Markus knew his total test average of the 5 tests he wouldn't need to guess, he could just use the mean equation again:

(85 + 92 + 82 + 94 + x) / 5 = y (test score average)

Whether Markus gets his 5th test score (x) or his total test average (y) he can plug in for each variable to find the other.

(B) 5 (x + 5) = 353 + x