Question

how many liters of a 90% acid solution must be mixed with a 15% acid solution to get 675 L of an 80% acid solution?

Answer 1

will give medal and fan plz help

Answer 2

Let M equal the gallons of the 90% mixing solution. Let F equal the gallons of the final solution. So: 
90 + M = F.

Also, the number of gallons of pure antifreeze in the final will equal the sum of the gallons of antifreeze in the two mixing parts: 

Original solution: ( 90 gal )*(0.15) = 13.5 gal [0.15 represents 15%]Mixing solution: M*0.90Final solution: F*0.80
So 13.5 + M*0.90 = F*0.80 

Now you have 2 linear equations and 2 unknowns, you can solve for M & F, using your favorite method: M = 585 and F = 675. Add 585 gallons of the 90% to get 675 gallons of 80% solution.

Answer 3

help

Answer 4

@pphalke
In what way are you confused?

Answer 5

aveline the problem in general

Answer 6

A will represent the liters of the 90% acid solution, and B will represent the liters of the 15% acid solution
A+B=675
Both add up to a total of 675 liters
We only want one unknown variable, so let's rearrange the equation:
B=675-A

Now for the equation. The coefficients represent the percent acid per liter.
0.90A + 0.15B = (675)(0.80)
Let's substitute (675-A) for B:
0.90A+0.15(675-A)=(675)(0.80)

Use the distributive property:

0.90A+101.25-0.15A=540

You should be able to solve from here.

Answer 7

when I collect like terms I get 0.75?
I subtracted 0.90-0.15
is that right

Answer 8

@Aveline

Answer 9

That's the correct coefficient for A. What about the rest of the equation?

Answer 10

I did 0.75A+101.25=540
then I subtract 101.25 from both sides
but I get a negative answer its -9585?? is it right

Answer 11

Aveline

Answer 12

Ok, so:
0.90A+101.25-0.15A=540
Combine A's
0.75A+101.25=540
Next, subtract 101.25

Answer 13

@Aveline I get a negative answer

Answer 14

What is 540-101.25?

Answer 15

438.75

Answer 16

Now divide that by 0.75A

Answer 17

585 @Aveline

Answer 18

Yes, you will use 585 liters of A, the 90% acid solution. It was mentioned that we needed to make 675 liters, and that A+B=675.
Can you find out how many liters of B we need?