the average (arithmetic mean) on three test scores is 77. what score is needed on the 4th exam to average 80?

Answer 1

If three scores averaged 77 then their total must equal three times 77 = 231. If you want the average to be 80 for 4 exams their total must equal four times 80 = 320. The difference between those two totals is what the fourth score must be to raise the new total. So 320 - 231 = 89. That is the score on the 4th exam you need to hit 80 average.

Answer 2

89.
(The average (arithmetic mean) on three test scores is 77.
So,total score of three test is,
77*3
=231.
For 80 being an average of 4 test,
Total score=80*4=320.
So, total score of 4 tests-total score of 1st 3 tests=score of 4th test.
That is,
320-231
=89 score is needed on the 4th exam to average 80.)

Answer 3

Let the scores of the first three be a,b & c
then according to your question
(a+b+c)/3=77

=> (a+b+c)=77*3=231

then let the fourth test score be x
then
(a+b+c+x)/4=80

=> (a+b+c+x) = 4*80 = 320

=> x=320-(a+b+c)

=> x=320 - 231

=> x=89.

the forth test score must be 89.

Answer 4

The mean of three test scores is 77 which implies the total aggregate of all the three test scores is 77*3 = 231

To get an average of 80 in four subjects the total aggregate required in the four subjects is 80*4 = 320.

Therefore the test score required in the fourth test is 320 -231 = 89.

Alternatively, logically speaking......
To get an average of 80 it means that he scores 80 each in the four tests. Therefore he needs to score 80 in the 4th paper plus some more score to make up for the loss in the previous three papers.
The loss to be recovered can be understood as follows.... he has scored 77 each in the three papers as the mean is 77. to score 80 each in those papers he needs 3 more in each paper and hence 9 in total...

Therefore 80(furth paper) + 9 (make up for loss in three previous papers) = 89.

Answer 5

77*3=231
231 is the sum of the three scores
(231+x)/4 = 80
231+x = 320
x=89

therefore the required score is 89

Answer 6

To average 80 on four tests the total score you need on all four tests is 4x80=320points. Since you averaged 77 on the first three tests, your total score on those three is 3x77=231. To get to the 320 points you need, you need to score 320-231=89. You need an 89 on the fourth test to average 80 on all four.

Answer 7

total score fo the three tests is 231. For average to be 80 over 4 tests, total score must be 320. So, 320 - 231 = 89, which is the score the 4th exam must be 89 marks. (:

Answer 8

first of all, since 77 is the average score
if we say a is the sum of the first 3 scores
we get

a/3 = 77
a = 231

Let x be the 4th exam score

(231+x)/4 = 80

multiply both sides by 4

231+x = 80(4)

231+x = 320

x = 320-231 = 89

ANSWER: 89

Answer 9

89, difference between 77 and 80 *4 added onto 77
12 +77

It could be 88 or 90 if your meant to round the numbers off, but 89 is exact

Answer 10

answer is 89

that is, 80 plus 3 times 80 minus 77