SOLUTION: You need a 90% alcohol solution. On hand, you have a 30 mL of a 55% alcohol mixture. How much pure alcohol will you need to add to obtain the desired solution?

Question 1149316: You need a 90% alcohol solution. On hand, you have a 30 mL of a 55% alcohol mixture. How much pure alcohol will you need to add to obtain the desired solution?
Found 4 solutions by Boreal, greenestamps, josgarithmetic, ikleyn:
Answer by Boreal(15235)   (Show Source): You can put this solution on YOUR website!
30 ml of 55% is 16.5 ml of pure alcohol.
add x ml of pure alcohol
the solution now has (30+x) ml of 90% alcohol, which is 16.5ml+ x ml pure alcohol
Those two are equal 27ml+.9x ml=16.5ml +x ml
10.5 ml=0.1 x
x=105 ml ANSWER
total solution is .9 (135)=121.5 ml pure alcohol
this is 105 ml pure added +16.5 there to begin with.
Answer by greenestamps(13200)   (Show Source): You can put this solution on YOUR website!

Here is a simple non-algebraic method for solving "mixture" problems like this.

You are starting with 55% alcohol and adding pure (100%) alcohol, stopping when you get to 90% alcohol.

(1) 90% is 7/9 of the way from 55 to 100. (55 to 90 is 35; 55 to 100 is 45; 35/45 = 7/9.)
(2) That means 7/9 of the mixture has to be what is being added.

So 7/9 of the mixture is the 100% alcohol and 2/9 is the 30 mL you started with.

(3) 2/9 = 30 mL --> 1/9 = 15 mL --> 7/9 = 105 mL

ANSWER: Add 105 mL of pure alcohol.

Answer by josgarithmetic(39618)   (Show Source): You can put this solution on YOUR website!
T=90
H=100
v=unknown, amount of pure 100% alcohol
L=55
U=30

-

, volume in mililiters, the pure alcohol to use
Answer by ikleyn(52790)   (Show Source): You can put this solution on YOUR website!
.

When I see such posts from @josgarithmetic, I become really sad and angry.

The educational value of such posts is 0 (zero, ZERO).

Moreover, posting such a nonsense, he actually blocks the posts from other tutors (from me, for example),
from which the reader / (the visitor) could learn something useful.

It is why I say that real contribution of @josgarithmetic is, actually, NEGATIVE at this forum.

Dear visitors, you will continue to get such GIBBERISH from him until YOU APPLAUD him.

RELATED QUESTIONS
You need a 90% alcohol solution. On hand, you have a 30 mL of a 40% alcohol mixture. How... (answered by josgarithmetic)
You need 1425 mL of a 30% alcohol solution. On hand, you have a 5% alcohol mixture. How... (answered by josgarithmetic)
You need a 55% alcohol solution. On hand, you have a 45 mL of a 30% alcohol mixture. You... (answered by josgarithmetic,richwmiller)
You need a 55% alcohol solution. On hand, you have a 30 mL of a 35% alcohol mixture. You... (answered by josgarithmetic)
You need 320 mL of a 55% alcohol solution. On hand, you have a 80% alcohol mixture. How... (answered by ewatrrr)
You need a 95% alcohol solution. On hand, you have a 55 mL of a 15% alcohol mixture. How... (answered by josgarithmetic)
You need 765 mL of a 30% alcohol solution. On hand, you have a 85% alcohol mixture. How... (answered by ewatrrr)
You need 1200 mL of a 25% alcohol solution. On hand, you have a 20% alcohol mixture. How... (answered by G8TORS)
You need 1235 mL of a 85% alcohol solution. On hand, you have a 5% alcohol mixture. How... (answered by addingup)