The student would have to score 100% on their next test to brung their average up to 90. Here is why; 90+84+86=260 (260+?)/4=90 (260+100)/4=90 360/4=90 This is done to get the mean (or average) of a group of numbers by adding all the numbers and dividing by the amount of numbers you added together. Here it is divided by 4 because of the three tests he has taken and the test he will take.
