You need 10% alcohol solution. on hand, you have a 390ml of a 5% alcohol mixture. you also have 75% alcohol mixture. how much of the 75% mixture will you need to add to obtain the desired solution

Remark

There is a short way of doing this problem, but I'm not sure how to do it. If you are interested, you could google for the answer to this kind of problem. In the meantime, there is one sure way of doing it.

Givens

390 mL of a 5% solution.

Enough 75% solution to satisfy the equation.

Desired result = 10%

Equation

C_75% * V + C_5% * 390 = C_10% * (390 + V)

Solution

75% * V + 5%*390 = 10% (390 + V)

75% * V + 0.05* 390 = 0.1(390 + V)

0.75 * V + 19.5 = 39  + 0.1 * V              

0.75 * V - 0.1*V + 19.6 = 39

0.65 * V  +  19.5 = 39  

0.65*V = 39 - 19.5

0.65*V = 19.5

V = 19.5 / 0.65

V = 30 mL of 75% alcohol

rick has $1400 and sally has $1500

step-by-step explanation:

to find amount of money rick has after 10 years :

principal = $1000 , time = 10 years , rate = 4% annually

to find amount of money sally has after 10 years :

her friend gives to pay her $50 per year, therefore money she has after 10 years = 50 × 10 = $500

also, sally gets $1000 after 10 years,

therefore, total amount of money sally has after 10 years = 500 + 1000 = $1500

so, after 10 years : rick has $1400 and sally has $1500