How many parts of 10% ointment be mixed with 2 parts of 15% ointment to get 12% ?

To find out how many parts of 10% ointment should be mixed with two parts of 15% ointment to get a 12% ointment, we can set up a mixture equation.

Let's denote:

x as the number of parts of 10% ointment to be mixed.

2 as the number of parts of 15% ointment already present.

According to the mixture equation, the total amount of the mixture will be the sum of the parts of each type of ointment:

Total parts of mixture = x (parts of 10% ointment) + 2 (parts of 15% ointment)

The total mixture should result in 12% concentration, so we can set up the equation:

0.10x + 0.15(2) = 0.12(x + 2)

Now, let's solve for x:

0.10x + 0.30 = 0.12x + 0.24

0.30 - 0.24 = 0.12x - 0.10x

0.06 = 0.02x

x = 0.06 / 0.02

x = 3

So, 3 parts of the 10% ointment should be mixed with 2 parts of the 15% ointment to get a 12% ointment.