20% ammonia solution and 70% ammonia solution were mixed to form 50%

Question

20% ammonia solution and 70% ammonia solution were mixed to form 50% ammonia solution. If 120 litres of 20% ammonia solution were used in the process, what was the volume of the 50% ammonia solution that was produced?

A. 80 litres
B. 180 litres
C. 200 litres
D. 240 litres
E. 300 litres

Source: Experts Global

A. 80 litres
B. 180 litres
C. 200 litres
D. 240 litres
E. 300 litres

Source: Experts Global

chetan2u · Accepted Answer

Weighted average method..
20.......50......70 so ratio of 20% to total =  \frac{70-50}{70-20}=\frac{2}{5}=\frac{120}{total} 
therefore total = 120*5/2=300

E

BrentGMATPrepNow · Answer

Let's use the answer choices to our advantage.

IMPORTANT CONCEPT : If  EQUAL VOLUMES  of 2 solutions are combined, the concentration of the resulting mixture will be the  AVERAGE  of the 2 solutions. 
Example: If 3 liters of a 10% alcohol solution are combined with 3 liters of a 30% alcohol solution, the resulting solution will be 20% alcohol. 
Likewise, if 11 liters of 6% alcohol solution are combined with 11 liters of a 7% alcohol solution, the resulting solution will be 6.5% alcohol.

So,  if  we added 120 liters of 70% solution to the 120 liters of 20% solution, then the resulting  240  liters of solution would be 45% ammonia (since 45% is the average of 70% and 20%)
However since we want the resulting solution to be GREATER THAN 45% ammonia, we need to add MORE THAN 120 liters of 70% solution 
In other words, the resulting solution will consist of MORE THAN  240  liters

Check the answer choices....the correct answer must be E

Cheers,
Brent

AkshdeepS · Answer

A---------B
20.........70
....\....../ 
......50.......
 / \ 
20.........30

\frac{A}{B}  =  \frac{2x}{3x}

Given : A : 2x = 120

x = 60

So, B = 3x = 3*60 = 180

A + B = C (50% ammonia solution)

120 + 180 = 300

Hence (E)

OR

120*0.2 + x(0.7) = (120 + x)0.5

Solving for x, we get,

x = 180 litres

120 + 180 = 300 litres (E)

ScottTargetTestPrep · Answer

Let n = the number of litres in the 70% ammonia solution. We can create the equation:

0.2(120) + 0.7n = 0.5(120 + n)

24 + 0.7n = 60 + 0.5n

0.2n = 36

n = 36/0.2 = 360/2 = 180

Therefore, the volume of the 50% ammonia solution is 120 + 180 = 300 litres.

Answer: E

GMATGuruNY · Answer

The percentage for the mixture (50%) is closer to the percentage for the 70% solution (70%) than to the percentage for the 20% solution (20%).
Implication:
The 70% solution must constitute MORE THAN HALF of the total, while the 120 liters of 20% solution constitutes LESS THAN HALF of the total:
 120 < \frac{1}{2}T 
 T > 240

Since the total volume must exceed 240 liters, only E Is viable.

E

12921 · Answer

20%_________50%__________70%

50-20=30
70-59=20
Distance Ratio=3:2

Therefore,Weight Ratio= 2:3

In 2:3- if 2 part is 120 Litres then 3 part will be 180 Litres. So total volume= 120+180=300Litres

Answer - (E)

Can,Will · Answer

dear experts need help.

I am not able to understand the part of question "If 120 litres of 20% ammonia solution were used in the process, " 
it is given that "20% ammonia solution and 70% ammonia solution were mixed to form 50% ammonia solution" then why we just make an equation 120 + 70 percent of x = 20 percent of (120+x)

bumpbot · Answer

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20% ammonia solution and 70% ammonia solution were mixed to form 50%

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