In a certain accounting class of 90 students 70% of the students took

everyone here is working too hard..
65--x---85
ratio is 3/7, difference is 20, hence 3x+7x=20, x=2
65+3x=65+3*2=71

Average \(= \frac{63 * 65 + 27 * 85}{90} = 45.5 +25.5 = 71%\)

Answer = B

Total students 90
% of students appear in exam on assigned date 70% & average score 65%
% of students appear in exam on make up date 30% & average score 85%

average score of entire class =(65+85)/2=75 when no. of students appeared in the exam that happened on different dates.
since here ratio is uneven and weight of students is more concentrated on the score of 65%
This further shows that the average score for entire class must be below 75%.
So, we can minimize the answer choices to option A,B & C whereas to get the exact value one needs to solve it.

From here we have to solve it :
since we have the ratio given (students appear on assigned date)/(students appear on assigned date)=7/3

Average score for entire class =(7*65+3*85)/10 =(455+255)/10=710/10=71

Answer is B

Bunuel I understand clearly that this is the formula- but are we supposed to be able to multiply and divide those numbers in under 3 minutes? Is there a shorter method?

For this question just attack the stem with pure arithmetic- really the important thing in this question is just knowing how to establish the numerator ( the total number of scores from students who took the exam on both assigned days and make up days)

average= sum/ # items

65 = x/63
65 x 63 = x

85= y/27
85 x 27 =y

[65 x 63] +[85 x 27] / 90 = 71

Since 70% of the students took the exam on the assigned day, 0.7 x 90 = 63 students took the exam on the assigned day and 90 - 63 = 27 students took the exam on the make-up day.
The average score for the students on the assigned day was 65% and the score for those on the make-up day was 85%. We can now determine the overall weighted average score:

[63(65) + 27(85)]/90 = (4095 + 2295)/90 = 6390/90 = 71

Answer: B

B

Average Score (63*65 + 27*85)/90 = 71

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