Question #c47d5

1 Answer
Aug 13, 2017

He needs 10 ml of the 30% solution, and 90 ml of the 10% solution. This will create 100 ml of 12% solution.

Explanation:

This is basically a system of equations problem. You can set it up like this:

Let x represent the amount of 30% solution needed and let y represent the amount of 10% solution needed

#0.3x+0.1y=12#
#x+y=100#

We know that 30% of x added to 10% of y must give us 12 ml of the acid. We also know that x and y must add to 100. Those are represented above.

Now you can use substitution to solve. In the second equation, x+y=100, we can solve for x to get x = 100 - y. Then if we sub that in to the first equation, we can solve:

#0.3x+0.1y=12#
#0.3(100-y)+0.1y=12#

#30-0.3y+0.1y=12#

#30-0.2y=12#

#-0.2y=-18#

#y=90#

We need 90 ml of the 10% solution, meaning we must need 10 ml of the 30% solution.