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Torry has submitted 2/5 of his homework assignments, and he received a

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Torry has submitted 2/5 of his homework assignments, and he received a  [#permalink]

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New post Updated on: 20 Oct 2014, 03:29
1
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Difficulty:

  45% (medium)

Question Stats:

64% (01:57) correct 36% (02:30) wrong based on 227 sessions

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Torry has submitted 2/5 of his homework assignments, and he received an average grade of 75 for those assignments. If he wishes to receive an average grade of 90 for all his homework assignments, the average grade for Torry's remaining homework assignments must be what percent greater than the average grade for the assignments he has already submitted?

A. 15%
B. 20%
C. 25%
D. 33 1/3%
E. 40%

My faulty solution:
First two HW assignments: x1 + x2 = 2*0.75
Wish five HW assignments: (x1 + x2) + (x3 + x4 + x5) = 5*0.9
2*0.75 + (x3 + x4 + x5) = 5*0.9
x3 + X4 + x5 = 5*0.9 - 2*0.75 = 3
(x3 + x4 + x5)/3 = 1
Therefore, the average of assignments x3, x4, x5 must be 100% and the percent increase from 75% to 100% is 25%.

Thanks in advance for your help.


Princeton Review Math Workout for the GMAT 2nd edition, p. 268, #10:

Originally posted by bdennis on 19 Oct 2014, 23:14.
Last edited by Bunuel on 20 Oct 2014, 03:29, edited 1 time in total.
Renamed the topic and edited the question.
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Re: Torry has submitted 2/5 of his homework assignments, and he received a  [#permalink]

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New post 22 Oct 2014, 02:14
9
1
First 2 assignments, average = 75, so total = 150

Last 3 assignments, let total = 3x

Setting up the equation

\(\frac{150 + 3x}{5} = 90\)

x = 100

To get the resultant average of 90, the last 3 assignment average should be = 100

\(Percentage = \frac{100-75}{75} * 100 = \frac{1}{3} * 100 = 33.33%\)

Answer = D
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Re: Torry has submitted 2/5 of his homework assignments, and he received a  [#permalink]

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New post 20 Oct 2014, 01:45
1
bdennis wrote:
Hi, I need some help understanding why my reasoning is wrong for this question from Princeton Review Math Workout for the GMAT 2nd edition, p. 268, #10:

Torry has submitted 2/5 of his homework assignments, and he received an average grade of 75 for those assignments. If he wishes to receive an average grade of 90 for all his homework assignments, the average grade for Torry's remaining homework assignments must be what percent greater than the average grade for the assignments he has already submitted?
a. 15%
b. 20%
c. 25%
d. 33 1/3%
e. 40%
Correct answer: d. 33 1/3%

My faulty solution:
First two HW assignments: x1 + x2 = 2*0.75
Wish five HW assignments: (x1 + x2) + (x3 + x4 + x5) = 5*0.9
2*0.75 + (x3 + x4 + x5) = 5*0.9
x3 + X4 + x5 = 5*0.9 - 2*0.75 = 3
(x3 + x4 + x5)/3 = 1
Therefore, the average of assignments x3, x4, x5 must be 100% and the percent increase from 75% to 100% is 25%.

Thanks in advance for your help.


your solution is correct till the last step.

Generally, to find by what percent x is greater than y, we use the following formula:

((x-y)/y)*100--------------------------------1)

now in this we have to find by what percent average of the remaining three tests is greater than the average of the first two test.

so here x=100 and y=75
substituting these values of x and y in the equation 1) we have

(25/75)*100 = 33(1/3)%
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Re: Torry has submitted 2/5 of his homework assignments, and he received a  [#permalink]

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New post 20 Oct 2014, 02:36
1
My solution:

0.4*75 + 0.6x = 90
30 + 0.6x=90
0.6x = 60
x= 100

100/75= 1.3333...

Ans: D
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Re: Torry has submitted 2/5 of his homework assignments, and he received a  [#permalink]

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New post 01 May 2017, 19:05
(2*75/5)+(3x/5)=90
x=100
(25*100)/75=33.3%
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Re: Torry has submitted 2/5 of his homework assignments, and he received a  [#permalink]

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