Question

Can anyone help me with half-life?

Answer 1

@phi An element has a half-life of 30 years. If 1.0mg of this element decays over a period of 90 years, how many mg would remain?

Answer 2

the equation is
\[ A= A_0\left(\frac{1}{2}\right)^\frac{t}{30} \]

that says if t is 30 you would get
\[ A= A_0\left(\frac{1}{2}\right)^\frac{30}{30} \\A= A_0\left(\frac{1}{2}\right)
\]
i.e. you would have 1/2 left, just as you are supposed to.

Answer 3

replace t with 90
and replace A0 with 1 mg

Answer 4

can you do that?

Answer 5

0.125 mg?

Answer 6

you should get (1/2) ^ (90/30)
90/30 is 3
so
(1/2)^3
which means 1/2 *1/2 *1/2 = 1/8

Answer 7

and yes 1/8 * 1 mg = 0.125 mg

Answer 8

so that's it?