Need Help With Algebraic Equation

[Furyous]

So, my GF called me here in Chile, from the US, and can't figure out how to do this problem... Any help would be appreciated, as it's got me stumped...

Streak Free window cleaner (F) is 20% alcohol. Sun Streak window cleaner (S) is 30% alcohol. How much of each should be mixed to make 100 oz. of window cleaner at 25% alcohol?

I've tried solving this with substitution method, and can't get anywhere. Can't figure out where the hell I'm going wrong....

[steff]

I don't understand you actually or else I'd help.

[Furyous]

Right then, this is the only thing that matters, ignore the rest....


Streak Free window cleaner (F) is 20% alcohol. Sun Streak window cleaner (S) is 30% alcohol. How much of each should be mixed to make 100 oz. of window cleaner at 25% alcohol?

[tim|away]

you should have two equations on your paper. let's say x is the amount of 20% alcohol and y the amount of 30% alcohol. for the sake of simplicity i'll leave away the units of measurement.

x + y = 100
(1) x = 100-y

20/100 * x + 30/100 * y = 100 * 25/100
(2) 1/5x + 3/10y = 25

use (1) to solve (2).

1/5(100-y) + 3/10y = 25
20 + 1/10y = 25
y = 50

x = 100-50 = 50

questions?

[hoos]

why do you always beat me to these questions, and then get them right all the time?

smarty pants :P

[nfc]

What Tim said...:P

[Furyous]

Yeah, thanks for the help fellas. I just figured it out as well. I started working on this damned problem late last night afte an emergency plea for help from my GF. I wasn't thinking clearly. Thank you for the help.... I appreciate it.