Atoms of element a decay to atoms of element b with a half-life of 20,000 years. if there are 10,000 atoms of a to begin with (and 0 atoms of b), how long will it take for there to be 2,500 atoms of a? a) 20,000 years b) 40,000 years c) 60,000 years d) 100,000 years

T = half life period of decay for atoms of element A = 20,000 years

N₀ = initial number of atoms of element A = 10,000 atoms

N = final number of atoms after time "t" = 2500 atoms

t = time of decay = ?

λ = decay constant = ?

decay constant is given as

λ = 0.693/T

λ = 0.693/20,000

λ = 0.00003465 years⁻¹

atoms after decay for time "t" is given as

N = N₀

inserting the values

2500 = (10000)

t = 40,000 years

so correct choice is

B) 40,000 years

igneous rocks also form where plates converge. the subducting plate melts as it sinks into the crust of the earth, and the melt rises into the overriding plate forming volcanoes. metamorphic rocks are formed mainly in the lithosphere, wherever there is high pressure and high temperature. -woods