Question: I need a clearer understanding of how to solve: Pierre, Paul, and Jacques bought 12 kg of apples. Peter wants a quarter of that and Paul wants 1/3 of that. How many kilograms will James have left?
Answer: 
Peter wants 12 * 1/4 = 3 kg of apples.
Paul wants 12 * 1/3 = 4 kg of apples.
Together, Peter and Paul want a total of 3 + 4 = 7 kg of apples.
So James will have 12 - 7 = 5 kg.