This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Electrolyte Imbalance, Subject name: Medicine
A 35 year old, 70 kg female presents with sodium =160 mEq/L. Calculate the free water deficit for this patient: 
Select and explain. 
A. 5 L, B. 12 L, C. 15, D. 20 L
A: 5 L
Answer: A: 5 L 
Explanation: Approximate percentage water of total body mass. Patient % Children 60 Non-elderly males 60 Non-elderly females 50 Elderly males 50 Elderly females 45 Water deficit=Total body water x (current sodium -140)/140 TBW(female) = 0.5 x weight = 35 L for the patient mentioned in question Water deficit =35 x (160-140)/140 Water deficit = 5 liters