13. An Olympic sized swimming pool when full contains 2,500,000 litres of water. To keep the swimming pool disinfected, the pool needs to maintain a chlorine concentration of 0.5ml of chlorine per litre of water. Assuming the swimming pool is emptied and re-chlorinated every day, how much chlorine is needed to disinfect an Olympic sized swimming pool for 5 days? (1 litre = 1000ml)