Latest IBM Aptitude Question SOLUTION: A substance is 99% water. Some water eveporates, leaving a substance that is 98% water. How much of the water evaporated?

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A substance is 99% water. Some water eveporates, leaving a substance that is 98% water. How much of the water evaporated?

Asked In IBM (12 years ago)

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Tijo Jose  (12 years ago)

50/99 of the total water evaporated.

Let evaporated water be x.
(99-x)/(100-x) = 98/100
Or, (100-x)/(99-x) = 100/98
Applying dividendo,
1/(99-x) = 2/98 = 1/49
Or, 99-x = 49
Or, x = 50.
Since there were 99 units of water available, and 50 units of water evaporated, 50/99 of the total water evaporated.

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Aditya sahu  (11 years ago)

Let's say we start with W units of water, and S units of other stuff.
We originally have 99% water, so

W 99
--- = ---
W+S 100

Now we want to reduce the water to some fraction, F, of the original
amount. And we want to end up with 98% water:

FW 98
---- = ---
FW+S 100

We can solve each of these equations for S:

W 99
--- = ---
W+S 100


100W = 99(W+S)

100W = 99W + 99S

W = 99S

W/99 = S

and

FW 98
---- = ---
FW+S 100

100FW = 98(FW+S)

100FW = 98FW + 98S

2FW = 98S

2FW/98 = S

Two things equal to the same thing are equal to each other, so

W/99 = 2FW/98

1/99 = 2F/98

98/(99*2) = F

0.495 = F

So 49.5% of the water remains, which means that 50.5% evaporated

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