## ctheowl 3 years ago Can anyone please help me? You need a 20% alcohol solution. On hand, you have a 400 mL of a 15% alcohol mixture. How much pure alcohol will you need to add to obtain the desired solution?

1. princeofwetlot

you can set upthe equation as: x mL of 100% alchohol + 400 mL of 15% alcohol = (x + 400) mL of 20% alcohol

2. satellite73

you have 15% of 400 ml = $$.15\times 400=60$$ ml of alcohol at present. if you add say $$x$$ ml of alcohol you will have $$60+x$$ ml of alcohol and $$400+x$$ ml of solution you want $$400+x$$ ml to be 20% alcohol, so set $60+x=.20(400+x)$ and solve for $$x$$

3. satellite73

probably easiest to multiply by 10 on both sides to get $600+10x=2(400+x)$ $600+10x=800+2x$ $8x=200$ etc

4. ctheowl

THANK YOU VERY MUCH!

5. satellite73

yw hope steps are clear