What is the percentage strength of tretinoin gel when you combine 15 g of 0.025% and 30 g of 0.01%?
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To determine the percentage strength of tretinoin gel when you combine different concentrations, you will need to calculate the total amount of tretinoin in the combined mixture and then determine the overall percentage strength.
First, let's find the total amount of tretinoin in each component:
For the 15 g of 0.025% tretinoin gel:
0.025% of 15 g = (0.025/100) x 15 = 0.00375 g
For the 30 g of 0.01% tretinoin gel:
0.01% of 30 g = (0.01/100) x 30 = 0.003 g
Now, add up the amounts of tretinoin from each component to find the total amount in the combined mixture:
0.00375 g + 0.003 g = 0.00675 g
Next, calculate the percentage strength of the combined mixture by dividing the total amount of tretinoin by the total weight of the mixture and multiplying by 100:
(0.00675 g / (15 g + 30 g)) x 100 = 0.00675 g / 45 g x 100 ≈ 0.015 g/g x 100 ≈ 1.5%
Therefore, the combined tretinoin gel contains approximately 1.5% tretinoin.