Question 423870
1. If we start with 4 pints of 50% developer, this means that we initially have equal parts developer and water, i.e. 2 pints of each. To dilute the mixture to 39%, how many pints of water do we need to add?
The initial ratio = 0.5 = 2 pints developer/4 pints solution
Final ratio = 0.39 = 2 pints developer/(4 + x) pints solution
Solve for x: 0.39(4 + x) = 2 -> 1.56 + 0.39x = 2 -> 1.128 pints water added
To help visualize this, imagine if we wanted to dilute from 50% to 25%, then we would need to add 4 pints of water.  This gives 2 pints of developer in 8 pints of solution for a ratio of 0.25.

2. If we start with 70.6 liters of 41% glucose solution, this means we have 0.41*70.6 = 28.946 liters of glucose.  How much 14.1% solution can we make?
Ratio = 0.141 = 28.946/x 
Solving for x gives x = 28.946/0.141 = 205.291 liters.