Let x and y be the quantities of the 2% and 7% alcohol solutions to be used to make 100ml of 5%, here we get the equation as,
⇒ x+y=100
or y=100−x
Now to get the quantity of the solutions we get the equation as,
⇒ 2%x+7%y=5%100
Now by substituting the value of y in terms of x we get,
⇒ 2%x+7%(100−x)=5%100
Here by removing the % sign from both the sides we get,
⇒ 2x+7(100−x)=5×100
⇒ 2x+700−7x=500
⇒ −5x=−200
⇒ x=40
as we know y=100−x
⇒ y=100−40
⇒ y=60
∴ Required answer is 60ml.