Phil took four tests in his chemistry class. His average score after

Question

Phil took four tests in his chemistry class. His average score after the first three tests was 85%. After his fourth test, Phil’s overall average dropped. What score did he get on his fourth test?

(1) The average score of Phil’s first two tests was 90%.
(2) After Phil’s fourth test, his overall average was 80%.

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agrasan · Answer

Phil took four tests in his chemistry class. His average score after the first three tests was 85%. After his fourth test, Phil’s overall average dropped. What score did he get on his fourth test?

(1) The average score of Phil’s first two tests was 90%.
 Insufficient 
We don't get any info to solve for 4th test. At best, we can determine the score for 3rd test from this.

(2) After Phil’s fourth test, his overall average was 80%.
 Sufficient 
We can solve for 4th test using average equation.

Hence,  (B)  is the answer.

poojaarora1818 · Answer

Solution:

Given: Phil's average score after the first three tests was 85%.

Let's consider the scores of Phil's are, x,y,z, and v. So, the average of the three would be \frac{ x+y+z}{3}  *100 = 85%(0.85), and the total of x,y,z is 2.5.

(1) The average score of Phil’s first two tests was 90%. Insufficient

Just knowing the average of two scores, we cannot tell his fourth score.

(2) After Phil’s fourth test, his overall average was 80%. Sufficient

Here we can see the average of the 3 scores is 0.85, and the sum is 2.5. And the average of four is 0.80, and the sum would be 3.2. So, the fourth score in the set would be 0.7.

Hence, Option B

Souradeep17 · Answer

Given after first 3 test his average score is 85% 
so if his test where out of X then he secured a total of 85/100 * 3x 
From Option 1, 
We don't see any clue with which we can get absolute value for the 4th score.
So, option 1 is clearly not sufficient

option 2 
Though from here we can find that the percentage of score for the 4th exam will be 65% we still won't be able to find the absolute value for it.
For example, if the exams were out of 100 
then the marks in 4th exam will be 65 but if it was in 200 then the score would be 130. Since the option specifically asks for score it should not be possible.

Hence i choose (E)

Missinga · Answer

Phil took four tests in his chemistry class. His average score after the first three tests was 85%. After his fourth test, Phil’s overall average dropped. What score did he get on his fourth test?
(a+b+c)/3=85/100 ; a+b+c=0.85*3=2.55 
d=?

(1) The average score of Phil’s first two tests was 90%.
We don’t know about fourth test.
Insufficient

(2) After Phil’s fourth test, his overall average was 80%.
(a+b+c+d)/4=80/100
a+b+c+d=0.80*4=3.2 
d=3.2-2.55 =0.65 
Sufficient

B

Phil took four tests in his chemistry class. His average score after

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Phil took four tests in his chemistry class. His average score after

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

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