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# Quick logs question Watch

1. Radioactive decay of a substance is modelled by:

, c is a positive constant, t is the time in years and R is the number of atoms.

It takes 5730 years for half of the substance to decay.

Find c.

Well I knosw t = 5730, but what is R? I know R = no. of atoms, but it doesnt say how many atoms there are when half of the substance has decayed, so is R = 1/2?

I know how to solve it using logs, just need to know what R = !

Thanks
2. (Original post by Chemhistorian)
Radioactive decay of a substance is modelled by:

, c is a positive constant, t is the time in years and R is the number of atoms.

It takes 5730 years for half of the substance to decay.

Find c.

Well I knosw t = 5730, but what is R? I know R = no. of atoms, but it doesnt say how many atoms there are when half of the substance has decayed, so is R = 1/2?

I know how to solve it using logs, just need to know what R = !

Thanks
What does the 1000 indicate? Once you realise this you'll know.

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Updated: December 6, 2010
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