Answer:
10% w/w = 10g/ 100g = x /3400g
x = amount of drug in 3400 g
or i would just say 10% of 3400 = 340 g of zinc oxide is needed to be 10% strength
now how much do you have to add of zinc oxide to get 15% strength??
so you will end up with 340g of original PLUS x amount of new zinc oxide = the total drug you will use.
so (340 + x)
and to find percentage of drug over entire medication ... you would say (340 + x) over (3400 + x)
and (3400 + x) = total medication with the additional zinc oxide you will want to add.
finally: total drug/ total medication(Rx) = the new percentage strength
sooo --> you wanted 15% to be the zinc oxide (drug)
(340 + x) / (3400 + x) = 15% drug
or better yet: (340 + x) / (3400 + x) = 15g/ 100g
since 15% is 15 out of 100
so CROSS MULTIPLY
and solve for x:
(340 + x) * 100 = (3400 + x) * 15
34000 + 100 x = 51000 + 15 x--> 85 x = 17000
x = 200 so 200 grams of zinc oxide must be added to the original to get your 15% of drug strength.
Explanation:
