Please Help ASAP

Question

You need a 15% alcohol solution. On hand, you have a 910 mL of a 10% alcohol mixture. You also have 80% alcohol mixture. How much of the 80% mixture will you need to add to obtain the desired solution?

Answer 1

if we say for x unit 10% alcohol mixture we need 1 unit 80% alcohol mixture which results as (x+1) unit 15% alcohol mixture:

x(10%) + (80%) = (x+1)*(15%)

if we divide each side by 5% to find x:

2x + 16 = 3x + 3

x = 13

So,

910ml / 13 units = 70 ml of 80% alcohol solution needed.