$ [2/25 - (3 \frac{3}{5} \div 1/6)] =2/25-(\frac{18}{5}\div 1/6)=2/25-(3/6\div 1/6)=2/25-2/25=0$ $ [2/25 - (3 \frac{3}{5} \div 1/6)] \times (\frac{\frac{1}{2} + \frac{1}{3} + ... + \frac{1}{20}}{\frac{1}{2} \times \frac{2}{4} \times \frac{4}{8} \times ... \times \frac{50}{100}})=0\times (\frac{\frac{1}{2} + \frac{1}{3} + ... + \frac{1}{20}}{\frac{1}{2} \times \frac{2}{4} \times \frac{4}{8} \times ... \times \frac{50}{100}})=0 $