Question

a doctor orders 150. ml of 1 (m/v) ibuprofen. if you have 8.0 (m/v) ibuprofen on had, how many milliliters do you need

Answer 1

A doctor orders 150 ml 1(m/v) ibuprofen.
(m/v ) denotes mass concentration,having unit mg/ml i.e. the weight of solute present per unit volume.
then 1 (m/v) ibuprofen means, 1 grams of ibuprofen present in 1ml of solution.
the desired amount of solution= 150 ml
in 150 ml 1 (m/v) ibuprofen, amount of ibuprofen present should be 150 grams.
again, the solution we have is 8 (m/v)ibuprofen that is having 8 grams per ml of solution.
so ml of ibuprofen solution that will be having 150 grams ibuprofen is 150/8 ml.
= 18.75 ml solution(that is the amount required from the 8(m/v) solution)   
this is having 150 grams ibuprofen in 18.75 ml, having mass concentration= 8 (m/v)
but we want mass concentration of 1 (m/v)
so we will add 150-18.75= 131.25ml water to this solution to make it 150 ml 1(m/v) ibuprofen.