The average rate of disintegrations from a certain radioactive sample is roughly 20 per minute. If you wanted to measure this rate to within 4%, for approximately how long would you plan to count

Two forces produce equal torques on a door about the door hinge. the first force is applied at the midpoint of the door; the second force is applied at the doorknob. both forces are applied perpendicular to the door. which force has a greater magnitude?