Question

How many ml of 20 percent acid should be added tp pure acid to make 20 ml of 50 percent acid ?

Answer 1

Let

x -----> ml of 20% acid

y ----> ml of pure acid

so

we have that

`\begin{gathered} x+y=20 \\ y=20-x\text{ ----> equation 1} \end{gathered}`
`0.20x+y=0.50(20)\text{ ----> equation 2}`

substitute equation 1 in equation 2

`\begin{gathered} 0.20x+(20-x)=0.50(20) \\ solve\text{ for x} \\ 0.20x+20-x=10 \\ x-0.20x=20-10 \\ 0.80x=10 \\ x=12.5\text{ ml} \end{gathered}`

The answer is 12.5 ml