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Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
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chetan86 wrote:
Solution Y is 40 percent sugar by volume, and solution X is 20 percent sugar by volume. How many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?

(A) 37.5
(B) 75
(C) 150
(D) 240
(E) 450


When solving mixture questions, I find it useful to sketch the solutions with the ingredients SEPARATED.

Start with 150 gallons of solution that is 40% sugar:

When we draw this with the ingredients separated, we see we have 60 gallons of sugar in the mixture.

Next, we'll let x = the number of gallons of solution X we need to add.
Since 20% of the solution X is sugar, we know that 0.2x = the volume of sugar in this solution:


At this point, we can ADD the two solutions (PART BY PART) to get the following volumes:


Since the resulting solution is 25% sugar (i.e., 25/100 of the solution is sugar), we can write the following equation:
(60 + 0.2x)/(150 + x) = 25/100
Simplify to get: (60 + 0.2x)/(150 + x) = 1/4
Cross multiply to get: 4(60 + 0.2x) = 1(150 + x)
Expand: 240 + 0.8x = 150 + x
Rearrange: 90 = 0.2x
Solve: x = 450

Answer: E

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Originally posted by BrentGMATPrepNow on 03 Aug 2018, 12:15.
Last edited by BrentGMATPrepNow on 19 May 2021, 07:09, edited 1 time in total.
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
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chetan86 wrote:
Solution Y is 40 percent sugar by volume, and solution X is 20 percent sugar by volume. How many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?

(A) 37.5
(B) 75
(C) 150
(D) 240
(E) 450



Answer = E = 450

Solution Y

Sugar ................ Water .............. Total

40 ............................ 60 .................. 100

60 .......................... 90 .................... 150

Say x litres of Solution x added; New equation would be

\(60+\frac{20x}{100}\) .............. \(90+\frac{80x}{100}\) ............ 150+x

New sugar concentration is 25%; setting up the equation

\(\frac{25}{100} (150+x) = 60 + \frac{20x}{100}\)

x = 450
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
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I did a slightly different differential method.

40----25----20
--15------5---

So Y has to be 5/20 of the new solution. Given Y = 150 gallons

150 = 5/20(total)
Total = 600
X = 600 - 150

Ans E) 450
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
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chetan86 wrote:
Solution Y is 40 percent sugar by volume, and solution X is 20 percent sugar by volume. How many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?

(A) 37.5
(B) 75
(C) 150
(D) 240
(E) 450


Weighted Average Method :

Let's add G gallons of solution X

So we have, \(\frac{G}{150}\) = \(\frac{40 - 25}{25 - 20}\)

\(G = 150 * \frac{15}{5}\)

\(G = 450\)


Algebraic Method:

\(0.20X + 0.40Y = 0.25(X +Y)\)

\(0.20X + 0.40Y = 0.25X + 0.25Y\)

\(0.5X = 0.15Y\)

\(X = \frac{0.15*150}{0.5}\)

\(X = 450\)
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
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chetan86 wrote:
Solution Y is 40 percent sugar by volume, and solution X is 20 percent sugar by volume. How many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?

(A) 37.5
(B) 75
(C) 150
(D) 240
(E) 450



Sol Y = 40% sugar---------------------Sol Mix = 25 % sugar-----------------Sol X = 20% sugar

Sol Y = +0.15 than Avg---------------Avg = 0.25------------------------------Sol X = -0.05 than avg

0.15 Y - 0.05 X = 0
0.15 Y = 0.05 X

X/Y = 0.15/0.05 = 3:1

X:Y:Total = 3:1:4

If Y = 150 Gallons then by ratio X:Y = 3:1

X/150= 3/1
X = 150 * 3 = 450 Gallons

Ans E
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Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
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(.4)(150)+.2x=.25(150+x)
x=450 gallons
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
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Hi All,

Mixture questions can also be answered with the Part/Whole formula:

In this case, we're dealing with Sugar/Total

Solution X = 20% sugar
Solution Y = 40% sugar

We're told to mix a certain amount of Solution X with 150 gallons of Solution Y to get a 25% sugar solution:

X = number of gallons of Solution X

[(.2)(X) + (.4)(150)] / (X + 150) = .25

Now, it's just algebra steps:

.2X + 60 = .25X + 37.5

22.5 = .05X

450 = X

Final Answer:

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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
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Your method is correct, and infact I find weighted average/mixture alligation method to be the best approach to solve such questions.


adkikani wrote:
Attachment:
2504 sol.jpeg
Bunuel niks18 chetan2u gmatbusters VeritasPrepKarishma

Quote:
Solution Y is 40 percent sugar by volume, and solution X is 20 percent sugar by volume. How many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?


I am trying to master concept of weighted average by scaling since I find it
very time efficient and applicable in multiple scenarios.

Please help if my approach is correct (with help taken from this blog.)


Posted from my mobile device

Posted from my mobile device
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Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
Attachment:
2504 sol.jpeg
2504 sol.jpeg [ 24.41 KiB | Viewed 27289 times ]
Bunuel niks18 chetan2u gmatbusters VeritasPrepKarishma

Quote:
Solution Y is 40 percent sugar by volume, and solution X is 20 percent sugar by volume. How many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?


I am trying to master concept of weighted average by scaling since I find it
very time efficient and applicable in multiple scenarios.

Please help if my approach is correct (with help taken from this blog.)
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
GMATPrepNow wrote:
chetan86 wrote:
Solution Y is 40 percent sugar by volume, and solution X is 20 percent sugar by volume. How many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?

(A) 37.5
(B) 75
(C) 150
(D) 240
(E) 450


When solving mixture questions, I find it useful to sketch the solutions with the ingredients SEPARATED.

Start with 150 gallons of solution that is 40% sugar:

When we draw this with the ingredients separated, we see we have 60 gallons of sugar in the mixture.

Next, we'll let x = the number of gallons of solution X we need to add.
Since 20% of the solution X is sugar, we know that 0.2x = the volume of sugar in this solution:


At this point, we can ADD the two solutions (PART BY PART) to get the following volumes:


Since the resulting solution is 25% sugar (i.e., 25/100 of the solution is sugar), we can write the following equation:
(60 + 0.2x)/(150 + x) = 25/100
Simplify to get: (60 + 0.2x)/(150 + x) = 1/4
Cross multiply to get: 4(60 + 0.2x) = 1(150 + x)
Expand: 240 + 0.8x = 150 + x
Rearrange: 90 = 0.2x
Solve: x = 450

Answer: E

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great explanation! this post deserves to be the most helpful expert reply in this thread :)
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
chetan86 wrote:
Solution Y is 40 percent sugar by volume, and solution X is 20 percent sugar by volume. How many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?

(A) 37.5
(B) 75
(C) 150
(D) 240
(E) 450


solution Y is 150 gallons of which sugar is 40% ; 60 gallon
and solution X is 20% sugar by vol let that be X.
given in question that many gallons of solution X must be added to 150 gallons of solution Y to create a solution that is 25 percent sugar by volume?

60+20/100*(x) = 25/100 * ( 150+x)
solve for x we get
60+.2x= 1/4 *(150+x)
x=450
OPTION E
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
X/Y = 40-25 / 25-20 = 15/5 = 3/1

25% is closer to 20%, meaning that 20% is weighted more heavily.

Therefore 3 * 150 = 450. Answer is E.
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
"35 second solution

Take weighted avg

VALUES            20.....................25........................40
WEIGHT'S                    150                     X

25-20 unit's  =  150
5 unit's = 150
therefore 40-25 unit's = 15 unit's => 3(150) => 450.

 ­
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Re: Solution Y is 40 percent sugar by volume, and solution X is 20 percent [#permalink]
Y: 0.4sugar, 0.6 remaining
X= 0.2sugar, 0.8 remaining

60+0.2X/(150+X)=0.25
=>60+0.2X=37.5+0.25X
=>0.05X=22.5
=> x=450
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