SOLUTION: Gerry mixes different solutions with concentrations of 25%, 40%, and 50% to get 200 liters fo a 32% solution. Also, it takes twice the liters of the 40% solution to equal the same

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: Gerry mixes different solutions with concentrations of 25%, 40%, and 50% to get 200 liters fo a 32% solution. Also, it takes twice the liters of the 40% solution to equal the same      Log On


   



Question 269223: Gerry mixes different solutions with concentrations of 25%, 40%, and 50% to get 200 liters fo a 32% solution. Also, it takes twice the liters of the 40% solution to equal the same liters of the 25% , find how mnay liters of each kind he uses.
I have set up a table, but do not understand how the 50% factors in. Please help. Thank you!

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = liters of 25% solution needed
Let b = liters of 40% solution needed
Let c = liters of 50% solution needed
given:
(1) a+%2B+b+%2B+c+=+200 liters
(2) a+=+2b liters
%28.25a+%2B+.4b+%2B+.5c%29%2F200+=+.32
%28.25a+%2B+.4b+%2B+.5c%29%2F200+=+64
(3) 25a+%2B+40b+%2B+50c+=+6400
Multiply both sides of (1) by 25
and subtract from (3)
(3) 25a+%2B+40b+%2B+50c+=+6400
(1) -25a+-+25b+-+25c+=+5000
15b+%2B+25c+=+1400
3b+%2B+5c+=+280
5c+=+280+-+3b
c+=+56+-+%283%2F5%29%2Ab
Going back to (1)
(1) a+%2B+b+%2B+c+=+200
2b+%2B+b+%2B+56+-+%283%2F5%29%2Ab+=+200
3b+-+%283%2F5%29%2Ab+=+144
15b+-+3b+=+720
12b+=+720
b+=+60
And, since
a+=+2b
a+=+2%2A60
a+=+120
(1) a+%2B+b+%2B+c+=+200
120+%2B+60+%2B+c+=+200
c+=+20
120 liters of 25% solution are needed
60 liters of 40% solution are needed
20 liters of 50% solution are needed
check:
%28.25a+%2B+.4b+%2B+.5c%29%2F200+=+.32
%28.25%2A120+%2B+.4%2A60+%2B+.5%2A20%29%2F200+=+.32
%2830+%2B+24+%2B+10%29%2F200+=+.32
64%2F200+=+.32
64+=+64+ OK