SOLUTION: Hi Evan and his 3 friends scored an average of 80 marks. If Evan had scored 99 marks their average score would be 86 marks. How many marks did Evan score. Thanks

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Question 1176374: Hi
Evan and his 3 friends scored an average of 80 marks. If Evan had scored 99 marks their average score would be 86 marks. How many marks did Evan score.
Thanks

Found 2 solutions by ikleyn, greenestamps:
Answer by ikleyn(52824) About Me  (Show Source):
You can put this solution on YOUR website!
.

Let E = Evan' scores

    R = the sum of scores of the 3 his friends.


Then you have this equation


    %28E+%2B+R%29%2F4 = 80,   or   E + R = 320     (1)


and this equation


    %2899+%2B+R%29%2F4 = 86,   or  99 + R = 344    (2).



Subtract equation (1) from equation (2)


    99 - E = 24

    99 - 24 = E

     E      = 75.      ANSWER

Solved.



Answer by greenestamps(13203) About Me  (Show Source):
You can put this solution on YOUR website!


An informal solution uses the same calculations as the formal algebraic solution shown by the other tutor.

There are 4 people, their average is 80. Evan scoring 99, instead of what he actually scored, would raise that average to 86.

The increase in the average is 6, so the increase in total points is 6*4=24.

So Evan's actual score was 99-24 = 75.