Assume that the galaxy is 10 gyr old, the rate of star formation in the past was proportional to e^-t/t, where t is time since the galaxy formed and t = 3 gyr. and stellar lifetimes are given by t(m) = 10 gyr (m/msun)^-3. calculate the fractions of all (a) 2msun and (b) 5msun stars ever formed that are still around today.

By dividing you can find the answer

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.