Question 248248
Having a work problem concerning dilutions, and therefore ratios.
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We took 30 microliters of a stock, and added it to 270 microliters of saline to make 300 microliters of a 1:10 dilution.

We then took this 300 microliters and added 100 microliters of another solution (with no active ingrediant) to that to form 400 microliters total.
 
2 questions regarding this: What would the second dilution (300 microliters + 100 microliters) be considered? 3:4?
And, what would the final dilution be? 
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Equation:
active + active = active
0.10*300 + 0*100 = x(300+100)
30 + 0 = 400x
x = 30/400
x = 3/40 
The ratio of active ingrediant to non-active in the final solution is 3:40
or 1:13 1/3
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Congratualate your co-workers
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Cheers,
Stan H.