ATPN order requires 500ml Of Dextrose 30%. You find that the pharmacy only stocks Dextrose 70%.
How much water will you need to add?

286 ml of water

Explanation:

Since 500ml Of Dextrose 30% is needed to be produced from Dextrose 70%. Let us assume that x ml of Dextrose 70% is mixed with water to get 500 ml of Dextrose 30%. Hence:

30% of 500 ml = 70% of x

70x = 15000

Dividing through by 70:

x = 214 ml

Therefore 214 ml of Dextrose 70% is used

The amount of water used is gotten using:

amount of water = Amount of Dextrose 30% - Amount of Dextrose 70%

amount of water = 500 ml - 214

amount of water = 286 ml of water