Radium has a half-life of 1,620 years. in how many years will a 1 kg sample of radium decay and reduce to 0.125 kg of radium?

1,620 years

3,240 years

4,860 years

6,480 years

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.

Moving down the ramp from 6 meters to

Which measure of an earthquake depends on how close you are to the focus?