GRE Prep Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
A student's average (arithmetic mean) test score on 4 tests
[#permalink]
09 Sep 2020, 10:54
09 Sep 2020, 10:54
Expert Reply
00:00
Question Stats:
94% (00:36) correct
5% (00:52) wrong based on 19 sessions
Hide Show timer Statistics
A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80?
(A) 80
(B) 82
(C) 84
(D) 86
(E) 88
(A) 80
(B) 82
(C) 84
(D) 86
(E) 88
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: A student's average (arithmetic mean) test score on 4 tests
[#permalink]
09 Sep 2020, 11:53
09 Sep 2020, 11:53
1
Carcass wrote:
A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80?
(A) 80
(B) 82
(C) 84
(D) 86
(E) 88
(A) 80
(B) 82
(C) 84
(D) 86
(E) 88
We can solve the question using the weighted averages formula:
Weighted average of groups combined = (group A proportion)(group A average) + (group B proportion)(group B average) + (group C proportion)(group C average) + ...
We want the TOTAL average to equal 80
4/5 of the 5 scores have an average of 78
Let x = average of the 1 remaining test, which is worth 1/5 of the total average.
We get: 80 = (4/5)(78) + (1/5)(x)
Multiply both sides by 5 to get: 400 = 312 + x
Solve: x = 88
Answer: E
Cheers,
Brent
Re: A student's average (arithmetic mean) test score on 4 tests
[#permalink]
10 Sep 2020, 00:10
10 Sep 2020, 00:10
Quote:
A student's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the student's average score on the 5 tests to be 80?
Step 1: Understanding the question
As the average of 4 tests is 78, it can be understood that in each 4 test, score is 78, 78, 78, 78.
When the fifth test is included, average is 80, hence, score in each 5 test is 80, 80, 80, 80, 80
Step 2: Calculation
Test score of each of first 4 test increased by 2, 2, 2, 2
Hence total increase in score of first 4 tests is 8
Fifth test must have a score of 80 + total increased score = 80 + 8 = 88
E is correct
