In a certain class of students, 25% received A's on the final exam and 2/3 of these students received A's in the class as a whole. If 15 students in the class received A's on the final exam but did not receive an A in the class, how many students did not receive an A on the final exam?
a 45
b 60
c 105
d 135
e 180
A grades
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Let T = total # of students in the classsanaa.rizwan wrote:In a certain class of students, 25% received A's on the final exam and 2/3 of these students received A's in the class as a whole. If 15 students in the class received A's on the final exam but did not receive an A in the class, how many students did not receive an A on the final exam?
a 45
b 60
c 105
d 135
e 180
25% received A's on the final exam
So, the number of "A on exam" students = (0.25)T
2/3 of these students received A's in the class as a whole
This means that 1/3 of the "A on exam" students did NOT receive an A in the class as a whole
So, the number of "A on exam" students who did NOT receive an A in the class as a whole = (1/3)(0.25)T
15 students in the class received A's on the final exam but did not receive an A in the class
In other words, (1/3)(0.25)T = 15
To solve quickly, first multiply both sides by 3: (0.25)T = 45
Then multiply both sides by 4: T = 180
So, there are 180 students in the class.
25% of them got an A on the final exam (so, 45 "A on exam" students)
This means the remaining 135 students did not get an A on the exam.
Answer = D
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This is an EITHER/OR group question.In a certain class of students, 25% received A's on the final exam and 2/3 of these students received A's in the class as a whole. If 15 students in the class received A's on the final exam but did not receive an A in the class, how many students did not receive an A on the final exam?
45
60
105
135
180
Every student EITHER received an A on the final OR didn't.
Every student EITHER received an A for the course OR didn't.
For an EITHER/OR group problem, use a GROUP GRID to organize the data.
Let YF = yes on the final, NF = no on the final, YC = yes for the whole class, and NC = no for the whole class.
There are two fractions in the question stem: 25%=1/4 and 2/3.
Since the product of the denominators = 4*3 = 12, let the TOTAL = 12x.
Here's the grid:
Now let's use the information in the question stem to complete as much of the grid as possible._______________YF______NF_______Total
YC:
NC:
Total:___________________________12x
Values in the grid have to add up horizontally and vertically.
As soon as we know 2 entries in a row or a column, we can calculate the remaining entry in that row or column.
25% received A's on the final exam:
Since (1/4)(12x) = 3x, we get:
2/3 of these students received A's in the class as a whole._______________YF______NF_______Total
YC:
NC:
Total:__________3x______9x_______12x
Since (2/3)(3x) = 2x, we get:
15 students in the class received A's on the final exam but did not receive an A in the class._______________YF______NF_______Total
YC:____________2x_______________
NC:____________x_________________
Total:__________3x______9x_______12x
In the grid above, this is the value of x.
Thus, x=15, implying that the total number of students who did not receive an A on the final = 9x = 9*15 = 135.
The correct answer is D.
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Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
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