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zw504
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A portion of the 85% solution of chemicals was replaced with 24 Jul 2016, 03:03
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we could just consider "weight" issue and establish "weight" equation:

(1-N)*(85-40)+N*(20-40)=0
N=9/13
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A portion of the 85% solution of chemicals was replaced with 29 Aug 2016, 10:38
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bmwhype2
A portion of the 85% solution of chemicals was replaced with an equal amount of 20% solution of chemicals. As a result, 40% solution of chemicals resulted. What part of the original solution was replaced?

A. 5/13
B. 6/13
C. 9/13
D. 13/9
C. 13/6
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Please find the solution as attached.
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File comment: www.GMATinsight.com
Sol7.jpg
Sol7.jpg [ 111.92 KiB | Viewed 2647 times ]

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A portion of the 85% solution of chemicals was replaced with 20 Sep 2016, 07:35
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I got 9/17
not sure why,

experts please help
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46fe73cb-3213-4b92-8d3e-bc3e1ef3b00a.jpg
46fe73cb-3213-4b92-8d3e-bc3e1ef3b00a.jpg [ 95.21 KiB | Viewed 2583 times ]

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A portion of the 85% solution of chemicals was replaced with 24 Sep 2016, 19:48
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0.85(1-x) + 0.20x = 0.40
0.85 -0.85x + 0.20x = 0.40
-0.65x = -0.45 --> x = 9/13
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A portion of the 85% solution of chemicals was replaced with 22 Dec 2016, 05:41
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KillerSquirrel


the new ratio is 20:45 = 4:9 ---> meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

:)
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Thanks for the solution but can somebody explain the logic step by step and slowly?

the new ratio is 20:45 = 4:9 ---> meaning that if we had 13ml [ 4x + 9x = 13 and for the sake of the solution x = 1 hence 13 ml ] of 85% solution

[13ml of 85% solution .... what someone should understand by this. If someone tries to find the 0.85 of 13 it will not get int value] we now have only 4ml [how this magic 4 came up] so the part that was replaced is 9/13. [by now totally lost]
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A portion of the 85% solution of chemicals was replaced with 19 Oct 2019, 10:35
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bigfernhead
Can someone explain to me killer squirrels method? my head is spinning.

Specifically, this part:

meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

KillerSquirrel
See attachment

the new ratio is 20:45 = 4:9 ---> meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

:)
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It means if we have a mixture of solution in the ration 4:9, lets say 4x of a and 9x of b amount. Total amount is now 13x, but initially the total amount was 13x of a (without mixing). After mixing the ratio is now 4:9, i.e out of total 13x (original a)only 4x of a is left in the solution, other 9x has been replaced with solution b.
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A portion of the 85% solution of chemicals was replaced with 13 Jan 2022, 07:07
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Bunuel
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A portion of the 85% solution of chemicals was replaced with an equal amount of 20% solution of chemicals. As a result, 40% solution of chemicals resulted. What part of the original solution was replaced?

A. 5/13
B. 6/13
C. 9/13
D. 13/9
C. 13/6

This is a weighted average question. Say x% of the solution was replaced --> equate the amount of chemicals: 0.85(1-x)+0.2*x=0.4 --> x=9/13.

Answer: C.
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Bunuel - Can you please explain why 1-x? what is the rationale behind this?
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A portion of the 85% solution of chemicals was replaced with 19 May 2025, 17:59
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