Answers:
To find a mean (average), you add all of the data together and divide by the total count of items you added. So now just take what you know, use X for the unknown and solve for X.
I'll start you out...
(87 + 81 + 88 + X)/4 = 87
YOU do the rest.
And shame on anyone out there who completely spoon feeds the answer.
92.
87 is right on the mean.
81 is 6 less than the mean.
88 is 1 more than the mean.
6-1=5, so the next test must be 5 more than the mean. Results in 92.
To check it, add up the numbers and divide by 4. Results in 87.
Not a traditional response, but it's been a while since I've done stats.
92. 87+81+88+92=348/4=87 So the score that the student must earn on the fourth test is 92.
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