Question

A container holds 3 liters of a 25% alcohol solution. One half

liter of the solution is withdrawn and replaced with one half

liter of pure alcohol. What is the percentage of alcohol in the

new mixture?

Answer 1

You are adding 1.5 litres of 100% alcohol to 25% solution to get 3 litres of mixture.

Let the % of mixture be $x$

$1.5×100\%+1.5×25\%=3×x\%$

$1.5+37.5=3x\%$

multiply both sides by 100

$39=3x$

$x=13\%$