Real life story problem

This is why you should learn arithmetic.

Question:

My son had a fever, and was taking Advil for infants.

According to the instructions, he needed 1.875 ml every dose.

However, we ran out with only 1.25 ml left, and only Advil for children was available.

How much Advil for children do I need to give my son?

Answer:

Since there is 50 mg in 1.25 ml of Advil for infants, he needs 50 x 1.875 / 1.25 = 75 mg of Ibuprofen.

He has already taken 1.25 ml, which has 50 mg.

So he still needs 75 - 50 = 25 mg more.

Advil for children has 100 mg per 5 ml, so I need to give him 25 / 100 x 5 = 1.25 ml more.