How much pure acid is in 400 ml of a 12% acid solution?

So what you basicaly need to find in this problem is to find out how much is 12% of 400mL. To find that you can multiply 400 and 0.12 :
400mL × 0.12= 48mL

You can also divide 400 by 100 to find how much 1% of 400 is:
400mL ÷ 100 = 4mL
1% of 400mL is 4mL
as we want to find how much 12% of 400mL is we can just multiply 4mL(1% of 400) by 12
4mL × 12 = 48mL
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He secknd step was the answer to them