Question

PLEASE HELP ME If a radioactive substance has an initial mass of 50 grams

Answer 1

Answer: $3.125\ g$

Explanation:

Given

Initial mass $A_o=50\ g$

half-life is $T_{\frac{1}{2}}=5\ years$

At any time the left amount is given by

$A=A_o2^{-\dfrac{t}{T_{\frac{1}{2}}}}\\\\\text{Insert the values}\\\\A=50\cdot 2^{-\dfrac{20}{5}}\\\\A=50\cdot 2^{-4}\\\\A=\dfrac{50}{16}\\\\A=3.125\ g$