Gunther is making 100 mL of an antibiotic cream that is 15% antibiotic. He is using 18% and 10% creams. What is the ratio of the 18% cream in the final mixture?

The ratio of the 18% cream in the final mixture is 1:1.6

Explanation:

Let the amount of the 18% cream be x and that of the 10% cream be y

x + y = 100••••••(i)

18% = 18/100 = 0.18

10% = 10/100 = 0.1

0.18(x) + 0.1y = 0.15(100)

0.18x + 0.1y = 15 •••••(ii)

from equation i, y = 100-x

Substitute this into i

0.18x + 0.1(100-x) = 15

0.18x + 10 - 0.1x = 15

0.18x - 0.1x = 15-10

0.08x = 5

x = 5/0.08

x = 62.5 mL

So, the ratio of the 18% cream to the final mixture will be;

62.5:100

= 62.5/100 = 2.5/4 = 1:1.6