Chlorination is used in industry for the purification of water; 1gm so

Hi...thanks for highlighting.
It was a typo. It is 0.3 and not 0.03!!
I corrected it..

Are you sure the question you typed is correct? Can you put up a screenshot from the original source? I think the question is ambiguous and options make no sense.

1 gm solution of chlorine removes half the germs in 1 liter of water. 150 liter of water will need 150 gm solution of chlorine to kill half the germs. Currently, the water has .3/150 *100 = .2% harmful substances.
Adding 150 gms of chlorine will make it .1% harmful substances.
Now the issue is that do we need another 150 gms of chlorine solution (which will bring the harmful substances down to .05%) or a small amount which will bring the harmful substance concentration down to 0.09% since we need to find the minimum amount of chlorine solution.

The options 1, 2, 3, 4, 5 are of no help!

Hello

Yes, the question is right. I am attaching the screenshot anyway.
And as per the explanation provided in the question source, that additional one gram is required to bring down the harmful substances to 0.05%.
Hence the answer is 2 grams.

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Is something wrong with the question?
If 1gm solution of chlorine will remove half of the germs in 1 liter of water, then 150 gms of chlorine will be required twice to purify 150 liter of water containing 0.3 liter of harmful substances.

Maybe we need to point out what is the minimum amount of chlorine in the solution. That would be 2 gm per liter.

Right, but the quantity of water given is 150 liters, not 1 liter. So 150 gms of chlorine solution will bring the harmful substances down to 50% of the original amount. Also, the options do not specify the units of measurement - 1 gm etc.
Something certainly wrong with this question.

here 1gm of chlorine is removing 50% germs.
So 0.3lts germs in 150 lts water comprises 0.2% germs
so to bring quantity of germs below .09% to be considered good solution we need 1gm chlorine
this 1 gm chlorine remove 50% of .2% germs
means still we have 0.1%germs for which we need another 1 gm of chlorine which again removes 50% of 0.1% germs to 0.05%/
which is obviously <0.09%germs
So total 2gms needed.
Ans B

I agree with you. I think the question must be worded to state that - "1 gram of chlorine cleans half of the impurities from every 1 litre of water". If the question is this, then, the answer would be B.

This is a poorly worded question. Can we rephrase the "1gm Chlorine is required to remove half the germs in 1 liter of water"? Or change the answer choices...

I am amazed the source is GMAT Prep

150 litres of water contains 0.3 litres of harmful substances ( i am assuming harmful as germs)
so 1 litre of water contains 0.3/150 litres of germs.

(1/2)^n * 0.3/150 < 0.09/100, where n number of grams of chlorine required.
=> (1/2)^n < 0.45
=> we need minimum of 2 gms of chlorine

This question has attained the 700 level rank because it is so poorly worded.

1. Calculate concentration in sample:

0.3L / 150L = 0.2%

2. Add subsequent pieces of 1g until suitable concentration has been reached:

0.2% --> we add 1g --> 0.1% --> we add 1g --> 0.05%

0.05% is lower than 0.09%, hence sufficient!

Answer: 2g (B).

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