Suppose the half life of element K is 20 minutes. If you have 200 g sample of K, how much of element K will be left after 60 minutes?

##25color(white)(i)g##
Recall that the formula for half-life is:
##color(blue)(|bar(ul(color(white)(a/a)y=a(b)^(t/h)color(white)(a/a)|)))##
where:
##y=##final amount
##a=##inital amount
##b=##growth/decay
##t=##time elapsed
##h=##half-life
To find the amount of the sample left after ##60## minutes, substitute your known values into the equation.
##y=200(1/2)^(60/20)##
Solve for ##y##.
##y=200(1/2)^3##
##y=200(1/8)##
##color(green)(|bar(ul(color(white)(a/a)y=25color(white)(i)gcolor(white)(a/a)|)))##