φ(1000)=1000×(1−12)×(1−15)=1000×12×45=400\varphi(1000) = 1000 \times \left(1-\tfrac{1}{2}\right) \times \left(1-\tfrac{1}{5}\right) = 1000 \times \tfrac{1}{2} \times \tfrac{4}{5} = 400φ(1000)=1000×(1−21)×(1−51)=1000×21×54=400.