The amount of substance left of a radioactive element of half life,

after a time, t, is given by:

Given that <span>potassium-40 has a half life of approximately 1.25 billion
years.
The number of years it will take for 0.1% of potassium-40 to remain is obtained as follows:

Therefore, </span><span>the maximum age of a fossil that we could date using 40k is
12.5 billion years.</span>
Answer: 62
Explanation: It's an equilateral triangle
The area of the rectangular part = 14 x 20 = 280 sq. cm
The area of the half circle = 1/2 (3.14 x 7^2) = 76.9 sq. cm.
Total area = 280 + 76.93 = 356.9 cm^2
That comes to 225.65 / 6.25
= 36.1 hours