Question 148535

Let x=score on fourth exam


So the average A of all 4 exams are

75, 79, and 81 
{{{A=(75+79+81+x)/4}}}



Since the average must be greater than or equal to 80, this means that the right side is greater than or equal to 80


{{{(75+79+81+x)/4>=80}}} Set the right side greater than 80



{{{75+79+81+x>=320}}} Multiply both sides by 4.



{{{x+235>=320}}} Combine like terms on the left side.



{{{x>=320-235}}} Subtract {{{235}}} from both sides.



{{{x>=85}}} Combine like terms on the right side.



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Answer:


So the answer is {{{x>=85}}} which means that the student must get an 85 or better on the 4th exam.