Let x represent Bob’s score on his fourth exam.
In this case, the unknown is the score on Bob’s fourth exam. To find the average of four exam scores, sum the four scores, then divide by 4.
This last result can be simplified by summing the three known exam scores. $7973_w102_h38.png$
To isolate x, multiply both sides of the equation by 4.
We need to isolate x once again, so we subtract 194 from both sides of the equation.
x + 194 − 194 = 284 − 194
x = 90