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megafan
Joined: 28 May 2009
Last visit: 15 Oct 2017
Posts: 137
Given Kudos: 91
Location: United States
Concentration: Strategy, General Management
Schools: Stern PT Fall'18 Booth PT '18
GMAT Date: 03-22-2013
GPA: 3.57
WE:Information Technology (Consulting)
B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
15%
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Question Stats:
80% (01:29) correct
20%
(01:58)
wrong
based on 874
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Jim needs to mix a solution in the following ratio: 1 part bleach for every 4 parts water. When mixing the solution, Jim makes a mistake and mixes in half as much bleach as he ought to have. The total solution consists of 18 mL. How much bleach did Jim put into the solution?
A. 1mL
B. 2mL
C. 3mL
D. 4mL
E. 5mL
A. 1mL
B. 2mL
C. 3mL
D. 4mL
E. 5mL
To solve this problem:
The ratio is 1:4, meaning there should be x parts bleach and 4x parts water. However, Jim put in half as much bleach as he should have, so he put in \(\frac{x}{2}\) parts bleach. So the equation would be:
\(\frac{x}{2} + 4x = 18\) \(=> x=4\)
This part is clear, however, according to the MGMAT Guide the correct answer is not \(4\), but it's \(\frac{4}{2}\), but we already used \(\frac{x}{2}\) in the equation.
Now, \(4(2) + 2 = 18\) which makes sense. However, my main concern is with the reasoning, that to solve the equation, we have already halved Jim's amount, and then we are halving it again. Please explain.
The ratio is 1:4, meaning there should be x parts bleach and 4x parts water. However, Jim put in half as much bleach as he should have, so he put in \(\frac{x}{2}\) parts bleach. So the equation would be:
\(\frac{x}{2} + 4x = 18\) \(=> x=4\)
This part is clear, however, according to the MGMAT Guide the correct answer is not \(4\), but it's \(\frac{4}{2}\), but we already used \(\frac{x}{2}\) in the equation.
Now, \(4(2) + 2 = 18\) which makes sense. However, my main concern is with the reasoning, that to solve the equation, we have already halved Jim's amount, and then we are halving it again. Please explain.
08 Apr 2015, 23:29
Kudos
Bookmarks
Hi All,
While this is an old series of posts, there is a rather straight-forward way to approach this question that is more about real-world math than anything else.
The original prompt tells us that Jim needs to mix a solution in the following ratio: 1 part bleach for every 4 parts water.
So, if we have 1 part bleach + 4 parts water we get 5 parts total mixture....
Next, we're told that when mixing the solution, Jim makes a mistake and mixes in half as much bleach as he ought to have.
So, he ACTUALLY mixed 1/2 part bleach + 4 parts water and gets 4.5 parts total mixture....
The total solution consists of 18 mL. How much did Jim put into the solution?
18 = (4.5)(4) so the 18mL is made up of 4 "sets" of the 4.5 parts mixture. This means there are 4(4) = 16 mL of water and 4(1/2) = 2mL of bleach.
GMAT assassins aren't born, they're made,
Rich
While this is an old series of posts, there is a rather straight-forward way to approach this question that is more about real-world math than anything else.
The original prompt tells us that Jim needs to mix a solution in the following ratio: 1 part bleach for every 4 parts water.
So, if we have 1 part bleach + 4 parts water we get 5 parts total mixture....
Next, we're told that when mixing the solution, Jim makes a mistake and mixes in half as much bleach as he ought to have.
So, he ACTUALLY mixed 1/2 part bleach + 4 parts water and gets 4.5 parts total mixture....
The total solution consists of 18 mL. How much did Jim put into the solution?
18 = (4.5)(4) so the 18mL is made up of 4 "sets" of the 4.5 parts mixture. This means there are 4(4) = 16 mL of water and 4(1/2) = 2mL of bleach.
GMAT assassins aren't born, they're made,
Rich
General Discussion
06 Nov 2012, 20:29
Kudos
Bookmarks
megafan
if you look at the equation that you've set up. you would notice that you actually added x/2 part of bleach in 4x water not x part. Thus if x=4, the amount of bleach is x/2=4/2.
It is not x that you are looking for, but the value that you used in mixture ie x/2
