SOLUTION: a student has grades on three examinations of 70,86,and 78. what must the student earn on a fourth examination in order to have an average of at least 80?

Question 250503: a student has grades on three examinations of 70,86,and 78. what must the student earn on a fourth examination in order to have an average of at least 80?
Answer by actuary(112) (Show Source): You can put this solution on YOUR website!
Since the definition of "average" is ave = sum of all scores divided by the number of scores, we have 80 =(70+86+78+fourth exaximation score)/4
So 320 = 234 + fourth examination score (multiply both sides of the equation by 4 and add the known scores)
So 320-234 = fourth examination score (subtract 234 from each side of the equation
so fourth examination must be greater than or equal to 86 in order to have an average of at 80.
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