SOLUTION: Maria added white vinegar solution of acetic acid in water. There are 2 strengths of white vinegar-a 5% solution and a 10% solution. How many millilitres of each solution must she

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Question 234400: Maria added white vinegar solution of acetic acid in water. There are 2 strengths of white vinegar-a 5% solution and a 10% solution. How many millilitres of each solution must she mix to make 50mL of a 9% vinegar solution?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = ml of 5% solution to be added
Let b = ml of 10% solution to be added
given:
Total ml of final solution = 50 ml
Ml of acetic acid in final solution, .09%2A50+=+4.5 ml
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In words:
( acetic acid in 5% solution) + (acetic acid in 10% solution)/ (total ml of solution) = 9%
(1) %28.05a+%2B+.1b%29%2F50+=+.09
(2) a+%2B+b+=+50
This is 2 equations and 2 unknowns, so it's solvable
Multiply both sides of (1) by 50
(1) .05a+%2B+.1b+=+4.5
(1) 5a+%2B+10b+=+450
Now multiply both sides of (2) by 5 and subtract from (1)
(1) 5a+%2B+10b+=+450
(2) -5a+-+5b+=+-250
5b+=+200
b+=+40
and, since
a+%2B+b+=+50
a+=+50+-+40
a+=+10
10 ml of 5% solution and 40 ml of 10% solution are needed
check answer:
(1) .05a+%2B+.1b%29%2F50+=+.09
(1) .05%2A10+%2B+.1%2A40%29%2F50+=+.09
%28.5+%2B+4%29%2F50+=+.09
4.5%2F50+=+.09
.09+=+.09
OK