400
Remember that in decimal division, the decimal point moves the same way in both numerator and denominator. 1/0.0025 = 1 ÷ 0.0025 = 10 ÷ 0.025 = 100 ÷ 0.25. Notice that 0.25 = 1/4 is the reciprocal of 4, so dividing by this is the same as multiplying by 4. Thus, 1/0.0025 = 100 ÷ 0.25 = 100 × 4 = 400.