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# 1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%

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General GMAT Forum Moderator
Joined: 15 Jan 2018
Posts: 732
Concentration: General Management, Finance
GMAT 1: 720 Q50 V37
1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%  [#permalink]

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31 May 2019, 11:00
1
8
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Difficulty:

95% (hard)

Question Stats:

33% (03:28) correct 67% (02:46) wrong based on 55 sessions

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1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60% alcohol. If x > y, how many integer values can x take?

A. 10
B. 20
C. 35
D. 13
E. 30

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Re: 1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%  [#permalink]

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31 May 2019, 12:39
3
x.........y
....60....
1.........3

$$\frac{x-60}{60-y}$$=3/1
x+3y=240...(1)
x=240-3y=3(80-y)

We have 2 constraints
1. x=<100
2. x>y
Also, x will be a multiple of 3

x can be 99,96.....63
At x=60, y=60....Hence x can't take value equal to 60 or lower than 60.
Total number of integer values x can take= [$$\frac{99-63}{3}$$]+1=13

DisciplinedPrep wrote:
1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60% alcohol. If x > y, how many integer values can x take?

A. 10
B. 20
C. 35
D. 13
E. 30
##### General Discussion
Manager
Joined: 25 Mar 2018
Posts: 89
Location: India
GMAT 1: 640 Q50 V26
GMAT 2: 640 Q50 V26
GMAT 3: 650 Q50 V28
GMAT 4: 690 Q50 V31
GMAT 5: 730 Q50 V40
GPA: 4
WE: Analyst (Manufacturing)
Re: 1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%  [#permalink]

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31 May 2019, 21:30
2
Question is clear but OA is surprising.

The equation on which question depends is

x + 3y = 4*60

So we can start x with 61, which is integer value. We don't bother about Y. Y can take any value integer or not.

So IMHO answer is (100-61)+1 , which is 40.

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Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9983
Location: Pune, India
Re: 1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%  [#permalink]

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13 Jun 2019, 03:51
1
DisciplinedPrep wrote:
1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60% alcohol. If x > y, how many integer values can x take?

A. 10
B. 20
C. 35
D. 13
E. 30

1 part x% alcohol + 3 parts y% alcohol -> 60% alcohol

Since x > y, x must be greater than 60% and y must be less than 60% so that they average out to 60.
The maximum value of x can be 100% (the entire solution can be alcohol).
So x can take any integer value from 61 to 100.

But it seems that the intent of the question is that x and y both should be integer values.

y --- 60 --------- x

Since we are mixing 1 part x with 3 parts y, average will be 1 unit away from y and 3 units away from x.
So if y = 59, x = 63
if y = 58, x = 66
and so on...
x will take values from 63% to 99% i.e. (3*21) to (3*33)
This means (33 - 21 = )12 + 1 = 13 multiples of 3

Check this post for the scale method of weighted avgs:
https://www.veritasprep.com/blog/2011/0 ... -averages/
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Location: India
GMAT 1: 650 Q42 V38
GPA: 4
Re: 1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%  [#permalink]

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31 May 2019, 20:43
nick1816 wrote:
x.........y
....60....
1.........3

$$\frac{x-60}{60-y}$$=3/1
x+3y=240...(1)
x=240-3y=3(80-y)

We have 2 constraints
1. x=<100
2. x>y
Also, x will be a multiple of 3

x can be 99,96.....63
At x=60, y=60....Hence x can't take value equal to 60 or lower than 60.
Total number of integer values x can take= [$$\frac{99-63}{3}$$]+1=13

DisciplinedPrep wrote:
1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60% alcohol. If x > y, how many integer values can x take?

A. 10
B. 20
C. 35
D. 13
E. 30

I don't get it. x and y are concentration in percent. 3 and 1 are the value of units.
the 2 equations will be
1x + 3y = ?
x+y=60.

So we have to find to the value of x for which it is greater than y and the first equation gives a valid number.
right?
Manager
Joined: 11 Aug 2017
Posts: 59
Re: 1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%  [#permalink]

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31 May 2019, 23:14
nick1816 wrote:
x.........y
....60....
1.........3

$$\frac{x-60}{60-y}$$=3/1
x+3y=240...(1)
x=240-3y=3(80-y)

We have 2 constraints
1. x=<100
2. x>y
Also, x will be a multiple of 3

x can be 99,96.....63
At x=60, y=60....Hence x can't take value equal to 60 or lower than 60.
Total number of integer values x can take= [$$\frac{99-63}{3}$$]+1=13

DisciplinedPrep wrote:
1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60% alcohol. If x > y, how many integer values can x take?

A. 10
B. 20
C. 35
D. 13
E. 30

Why x has to be less than or equ. 100? i could not understand. please guide??
Manager
Joined: 01 Oct 2018
Posts: 112
Re: 1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%  [#permalink]

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12 Jun 2019, 17:51
nick1816 wrote:
x.........y
....60....
1.........3

$$\frac{x-60}{60-y}$$=3/1
x+3y=240...(1)
x=240-3y=3(80-y)

We have 2 constraints
1. x=<100
2. x>y
Also, x will be a multiple of 3

x can be 99,96.....63
At x=60, y=60....Hence x can't take value equal to 60 or lower than 60.
Total number of integer values x can take= [$$\frac{99-63}{3}$$]+1=13

DisciplinedPrep wrote:
1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60% alcohol. If x > y, how many integer values can x take?

A. 10
B. 20
C. 35
D. 13
E. 30

Why x has to be less than or equ. 100? i could not understand. please guide??

Maximum value of aclhogol in unit is 100%
Re: 1 unit of x% alcohol is mixed with 3 units of y% alcohol to give 60%   [#permalink] 12 Jun 2019, 17:51
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