Hello!
To solve this problem you should use the allegation method or X method. To set up the X method:
- put the more concentrated solution at the top left (25%)
- put the less concentrated product at the bottom left (5%)
- place the desired concentration (18%) in the middle of the X.
Subtract along the "X" lines to obtain to obtain the number of parts on the right: 25-18=7 ; 5-18 = 13
Can you imagine the X lines ? They are like the diagonals of the rectangle.
- add the number of parts on the right to find the total number of parts 13 (parts of 25% solution) + 7 (parts of 5%solution) = 20 parts of 18 % solution. Now you know that to obtain 20 ml of 18% sol you have to mix 13 ml of 25% with 7 ml of 5% solution and you can calculate how many ml from those 2 solution you have to mix to obtain 500 ml:
7x500/20 = 175 ml of 5%sol
13x500/20 = 325 ml of 25% sol
should be mixed to obtain 500 ml of 18 % sol. I hope this helped you to remember the allegation (X, rectangle) method used to solve these type types of problems 🙂
