Answer:
3
Explanation:
Applying,
[tex]2^{n'}[/tex] = R/R'............... Equation 1
Where n' = number of halflives that have passed, R = Original atom of the substance, R' = atom of the substance left after decay.
From the question,
Given: R = 40 atoms, R' = 5 atoms
Substitute these values into equation 1
[tex]2^{n'}[/tex] = 40/5
[tex]2^{n'}[/tex] = 8
[tex]2^{n'}[/tex] = 2³
Equation the base,
n' = 3
