Aradioactive substance has a half-life of 5 million years. what is the age of a rock in which 25% of the original radioactive atoms remain?
choose one answer.
a. 2.5 million years
b. 5 million years
c. 15 million years
d. 10 million years

Hence, the age of rock in which 25% of the original amount remain is:

10 million years.

A radioactive substance has a half-life of 5 million years.

What is the age of a rock in which 25% of the original radioactive atoms remain?

Let x be the initial amount of the substance.

Hence, 25% of the initial amount is:

x/4

i.e. in the table form the age could be represented as:

  Years                                      Amount left

5 million years                              x/2      

10 million years                             x/4.

Hence, the age of rock in which 25% of the original amount remain is:

10 million years.

the answer is b: 18

step-by-step explanation:

use the pythagorean theorem to .

a^2+b^2=c^2

plug 18 for "r"

the 2 legs are 18 and 24

18^2+24^2=c^2

324+576=c^2

900=c^2

c=30

30-12=18

18 is the radius

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