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There are three testing tubes A, B and C each with 10, 20 and 30 grams of pure water. You pour 10 grams of salt water with x% concentration into Tube A, fully mix it, take out 10 grams of the mixture and pour it into Tube B. After fully mixing Tube B, take out 10 grams of mixture from Tube B and pour it into Tube C. The final salt concentration in Tube C is 0.5%. What’s the salt concentration of the solution that you first poured into Tube A?

 Jan 11, 2021
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The  amount of the first salt concentration   =  x /10    where x is in grams

 

Final  salt concentration (per gram)  in Tube A  after  mixing =   x / (10 + 10)  = x /20

 

So....the amt  poured into   B *  concentration per gram  =  10 grams *  (x/20)  =      x/2  grams

 

So....the  final concentration  in   B   is    (x/2)  /  (10 +20)  =   =   x/60

 

And   the amout  poured into C * concentration  =  10 ( x/60)  =  x/6   grams

 

So....the final concentration in C  is    (  x/6) / (10  + 30)  =  x/ 240

 

x/240  = .005

 

x = 240 * .005  =  1.2 

 

So....the first  salt concentration   = 1.2  / 10     =   12% 

 

 

cool cool cool

 Jan 11, 2021

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