What is the percentage of radioactive nuclei left after 3 half lives pass?

The twister and runaway train are two coasters at the same amusement park. both coasters start at the same height. the coaster for the twister is twice the mass of the coaster for the runaway train. which roller coaster has greater gravitational potential energy at the start of the ride?

How does the motion of particles in a gas change as the gas cools

Consider the story you just read. all but one of the choices below indicate that something is living.