Can someone please explain this for statistics

Bismuth-210 is an isotope that radioactively decays by about 13% each day, meaning 13% of the remaining bismuth-210 transforms into another atom (polonium-210 in this case) each day. if you begin with 233 mg of bismuth-210, how much remains after 8 days?

Which statement is always true? a. square bcdf is a rectangle. b. rectangle gjkm is a square. c. quadrilateral stpr is a trapezoid. d. parallelogram abcd is a rhombus.

The variable in a relation who’s value depends on the value of the independent variable is called what?