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A rock once contained 1.0 mg of uranium-238, but now contains only 0.25 mg. Given that the half-life for uranium-238 is 4.5 x 10^9 (4.5 billion) years, how old is the rock?​

Respuesta :

Answer:

9 x 10 ^9 yrs    ( 9 billion years <=====older than Earth !)

Explanation:

.25 = 1.0 (1/2) ^n

.25 / 1.0 =   = (1/2 )^n

log .25 =  n log 1/2

n = 2 half lives

2 * 4.5 x 10^9 =   9 x 10 ^ 9 yrs

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