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The answer is- 0.0014 fraction of the 40K decay in 1.85 million years.

The decay rate tells us the amount of substance left after decay at time t. It is calculated using  the formula-

[tex]N = N_0 e^\frac{-t}{T_1_/_2}[/tex]

Where

N is the final amount left.

N0 is the initial amount of sample

t is the time

T1/2 is the half life.

What is the half life of 40 K?

  • The Half-life of 40K is [tex]1.28 * 10^9\ years[/tex].
  • Now , t = 1.85 million years = [tex]1.85* 10^6[/tex] years.
  • The fraction that decay is expressed as (N/N0) and is calculated as-[tex]\frac{N}{N_0} = e^\frac{-(1.85 *10^6)}{(1.28*10^9)} = e^{-0.00145} = 0.9986[/tex]
  • Next, let the initial amount be 1. Thus, the fraction that decay is-[tex]1-\frac{N}{N_0} = 1- 0.9986 = 0.0014[/tex]
  • Hence, 0.0014 fraction of the 40K decayed in 1.85 million years.

To learn more about decay rate, visit:

https://brainly.com/question/1160651

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