Answer:
1034 yrs
Explanation:
The equation to use in this question is:
t = -2.303/k log (A/A₀) where
A= present number of disintegrations
A₀ = intial number of disintegrations
k = decay constant
The decay constant we will obtain it from the given hal-life:
k: 0.693/t₁/₂, t₁/₂ = half-life ⇒
k: 0.693 / 5730 y = 1.209 x 10⁻⁴ /y⁻¹
t = - 2.303 / 1.209 x 10⁻⁴ /y⁻¹ x log (13.1/15.3) = 1034 yrs