A person measures the depth of a well by measuring the time interval between dropping a stone and receiving the sound of impact with the bottom of the well. The error in his measurement of time is dT = 0.01 seconds and he measures the depth of the well to be L = 20 meters. Take the acceleration due to gravity g=10ms−2 and the velocity of sound is 300 ms−1. Then the fractional error in the measurement, dL / L, is closest to