00:01
A pharmacist has 200 milliliters of a solution that has 40 % active ingredient.
00:06
How much pure water would she need to add to get the solution to be 25%.
00:13
Well, let's first figure out how much active ingredient we have in the original solution.
00:20
So this is going to be equal to.
00:24
So it's just 200 times 40%, which is going to be 80.
00:31
So this is going to be our initial amount that we have.
00:36
Well, if we want to get 25%, it's going to be our initial over our solution, or i should say our total amount, but in this case, since we're not adding any more active ingredient, it would just be initial.
00:49
But our solution, let's see what that's going to be.
00:53
So solution should be, well, we start at 200 milliliters, and we want to add just some amount of water, w.
01:00
So let's just go ahead and replace that.
01:03
So it should be 200 plus w.
01:06
And then we had i is 80...