Radioactive material 'A' has decay constant '8 λ' and material

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Radioactive material 'A' has decay constant '8 λ' and material 'B' has decay constant 'λ'. Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material 'B' to that 'A' will be
1 ?
e

Given,
λ_A = 8λ, λ_B = λ

N_B =	N_A
	e

⇒ N₀e^-λB^t

= N₀	e^-λA^t
	e

e^-λt = e^-8λte^-1
e^λt = e^{8λt - 1}
Comparing both side powers
-λt = -8λt - 1
- 1 = 7λt

t = -	1
	7λ

The best possible answer is

t =	1
	7λ