Answer: Between 1 and 2.
Explanation:
Half life is the amount of time taken by a radioactive material to decay to half of its original value.
[tex]a=\frac{a_o}{2^n}[/tex] ............(1)
where,
a = amount of reactant left after n-half lives = 40
[tex]a_o[/tex] = Initial amount of the reactant = 100
n = number of half lives
Putting in the values we get:
[tex]40=\frac{100}{2^n}[/tex]
[tex]2^n=2.5[/tex]
taking log on both sides
[tex]nlog(2)=log(2.5)[/tex]
[tex]n=1.32[/tex]
Thus half-lives that have elapsed is between 1 and 2
