A big container is 30% full with water. If 18 liters of

Question

A big container is 30% full with water. If 18 liters of water is added, the container becomes 3/4 full. What is the capacity of the big container?

A) 36 liters
B) 40 liters
C) 45 liters
D) 54 liters
E) 60 liters

wahed · Accepted Answer

This is a classic two equations, two unknowns type question. You could set up two equations, and use brute fore to solve. BUT, this is not what a smart test taker should do. Pattern recognition is what's being tested here.

Notice that answers A, B, and E, are divisible by 4, the others are no. So you can eliminate choices C, and D since 3/4 of these choices will not result in a whole number.

Since the answer choices are in chronological order, test the middle choice - choice B

notice that 3/4 of 40 is 30. Easy. If you subtract 18 from 30, you get 12. 12/40 reduces to 3/10 - 30%. Voila choice B satisfies the conditions of the question. Choice B is the correct answer.

Remember the GMAT isn't designed to test your math skills, it's designed to test critical thinking and your ability to recognize patterns and find the easy way of solving a problem. Look for the easy answers.

Cheers,
Wahed

rajeevrks27 · Answer

30% full with water can be written as 30C/100 or 3C/10 , where C is the capacity of the cylinder
18 liters of water is added, the container becomes 3/4 full
3C/10 + 18 ltr = 3C/4
 3C/4 - 3C/10 = 18 ltr
 C = 40 ltr
B is correct
try doing this question in ur mind..it will help u speed up the calculation and save time.

Bunuel · Answer

A big container is 30% full with water and after 18 liters of water is added, the container becomes 75% full. Hence these 18 liters account for 45% of the container, which means that the capacity of it is 18/0.45=40 liters.

OR:  if the capacity of the container is x liters then: 0.3x+18=0.75x --> x=40 liters.

Answer: B.

subhajeet · Answer

Ans is B
let x be the capacity 
so we have 0.75x = 0.3x+18 on solving we get x = 40

manalq8 · Answer

.3x + 18 = .75x

18=.75x _ .3x

18= .45x

18/.45 = x

multiply the numerator and the denominator by 100 to make it easier to solve.

1800/45=x

x= 40

hope this helps

vaibhavw · Answer

(30 / 100) x + 18 = 3/4 x

0.3x + 18 = 0.75x

18 = 0.75x - 0.3x

18 = 0.45X

x = 18 / (4.5/10)

x = 180 / 4.5

x = 40

Ans: B

IdiomSavant · Answer

Container starts at 30% or 3/20 then water is added to bring it to 3/4 full or 15/20.

15/20 – 3/20 means 9/20 water was added (18 liters).

Cross multiply.

18/x = 9/20

18 * 20 = 360 divided by 9 = 40

ScottTargetTestPrep · Answer

Letting n = the capacity of the container, we can create the equation:

3n/10 + 18 = 3n/4

Multiplying by 20, we have:

6n + 360 = 15n

360 = 9n

40 = n

Answer: B

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