SOLUTION: Mark's average (arithmetic mean) on four tests is 75. What grade does he need on his fifth test to raise his average to an 80? I need help on this question from an online assig

Question 294484: Mark's average (arithmetic mean) on four tests is 75. What grade does he need on his fifth test to raise his average to an 80?
I need help on this question from an online assignment, and it ends tonight so please hurry to answer this
Thank you
Found 2 solutions by Fombitz, richwmiller:
Answer by Fombitz(32388) (Show Source): You can put this solution on YOUR website!
1.
2.
where J,K,L,M are the grades from the first 4 tests, N is the next test grade.
From eq.1,

Use that in eq.2,

He needs to get 100 on his next test.
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
I was about to answer this out of turn, but then I saw the ending " please hurry to answer this."
You do realize we are volunteer tutors. We don't get paid.
Why should we put your problem ahead of the others who were here first?
I will give you a few hints.
What was the total of his first 4 tests?
Add that to his new average (x) and divide by 4+1
What will you set it equal to?
A second way
What will the new total be if he gets an average of 80 on 5 tests?

A third way
Add up every time he missed 80 on the first four tests and add that to 80 for the grade he has to get on the fifth test.
Hint: He isn't going to do it. Possible but not likely.
RELATED QUESTIONS
Mark's average (arithmetic mean) on four tests is 75. What grade does he need on his... (answered by stanbon)
If a student wanted to raise his overall grade by 5% and had an average of 75% over four... (answered by checkley77)
Larry's average (arithmetic mean) score on the first four of five tests is 88. If Larry... (answered by alicealc)
Michaels average score in four tests is 65 if he want to raise his overall average by 5... (answered by josgarithmetic)
Ryan has scored 74,86 ,75 ,69 and on his previous four tests. What score does he need on... (answered by reviewermath)
After six biology tests, Ruben has a mean score of 73. What score does Ruben need on the... (answered by josgarithmetic,greenestamps)
Andy's average grade for his four tests in math class is 87%. What grade does he have to... (answered by fractalier)
On his last three math tests, mark scored 85,95, and 80. What grade must he get on his... (answered by JBarnum)
On his last 3 math tests, Mark scored 85,95 and 80. what grade must he get on his next... (answered by Fombitz)