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buddyl91 buddyl91
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11 years ago
could somebody explain me how to solve this problem step by step, please? thank you!!
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ton
wrote...
#1
11 years ago
water has no saline of course so its concentration is 0%

now the equation is built as follows:

(amt of water)*(% concentrate) + (amt of solution)*(% concentrate) =

(total amt of fluid)*(% concentrate)

x*0% + 1*5% = ( x+1)*(2%)

x*0 + 1*.05 = .02( x+ 1)

.05 = .02x + .02

.05 - .02 = .02x

.02x = .03

x = .03 / .02

x = 3/2 = 1.5

x = 1.5 liters = answer

check

x*0 + 1*.05 = .02( x+ 1)

0 + .05 = .02( 1.5 + 1)

.05 = .02(2.5)

5/100 = (2/100)*(25/10)

5/100 = 2*25/100*10

5/100 = 50/1000 true
wrote...
#2
11 years ago
Okay, I'm in grade eight, and I had a bit of trouble with this, but I eventually got it.

First of all, you need to know what 5% of 1000 is (It's 50)

And also know what 2% of 1000 is (It's 20)


So to do this, you must do some cross-multiplying.

This is what I wrote down on my paper:

50/(1000+X)=20/1000
20(1000+X)=50(1000)
20000+20X=50000
20X=30000
X=1500

Now you do the equation, substituting for X=
50/(1000+1500)

X is the amount of water you would add, so 1500 is your answer.
wrote...
#3
11 years ago
1. A 5% saline solution means that there are 50 grams (g) of salt in 1000 milliliters (ml) of solution.

2. We need to know the number of ml, v, to add to the 1000ml to make the concentration 2% or 0.02.

Therefore the equation is: 50 / (1000 + v) = 0.02
Solving for v:
multiply both sides by (100 + v)
50 = 0.02(1000 + v)
50 = 20 + .02v
30 = .02v
1500 = v
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