the half-life of a parent atom is 10 years. if an orginial sample of a rock has 50 parent atoms, how many daughter atoms will there be after 40 years?

The picture below shows two galaxies. spiral galaxy and elliptical galaxy which of these statements best describes a similarity between the two galaxies? (2 points) both have elongated centers. both have centers shaped like bars. both change their shape from time to time. both are held together by gravitational forces.