Question 344495
How much 90 percent vinegar do you have to add to a gallon of 5 percent vinegar to get 20 percent vinegar?
You have 1 gallon of 5%
You need to add x gallons of 90%
The result will be (x+1) gallons of 20%

{{{1*0.05 + x *0.9 = (x+1)*0.2}}}
{{{0.05 + 0.9x = 0.2x + 0.2}}}
{{{0.7x = 0.15}}}
{{{x = 0.15/0.7}}} gallons of 90%
{{{x = 0.214}}} gallons
Make sense?


You can paint a certain room in 9 hours. Your brother can do it in 8 hours. How long does it take the two of you working together?
He can do you cna do 1/9 of the job in an hour. He can d0 1/8
Together you can do {{{1/9 + 1/8 = 8/72 + 9/72 = 17/72}}} of the job in an hour
{{{x * 17/72 = 1}}}
{{{x = 72/17 = 4.235}}} hours