You start with 420 mg of isotope which has half life of 20 days. How many mg will be left after 40 days

105 mg

Explanation:

The following data were obtained from the question:

Original amount (N₀) = 420 mg

Half life (t½) =20 days

Time (t) = 40 days

Amount remaining (N) =..?

Next, we shall determine the rate constant K, for the disintegration.

This can be obtained as follow:

Half life (t½) =20 days

Rate constant (K) =?

K = 0.693/ t½

K = 0.693/20

K = 0.03465 /day

Finally, we shall determine the amount remaining after 40 days as follow:

Original amount (N₀) = 420 mg

Rate constant (K) = 0.03465 /day

Time (t) = 40 days

Amount remaining (N) =..?

Log(N₀/N) = kt/2.3

Log (420/N) = (0.03465 x 40)/2.3

Log (420/N) = 1.386/2.3

Log (420/N) = 0.6026

420/N = antilog (0.6026)

420/N = 4

Cross multiply

420 = N x 4

Divide both side by 4

N = 420/4

N = 105 mg

Therefore, the amount remaining after 40 days is 105 mg.

alienation, transformation, consumption, and the relativity of truth.

you can choose any one of these, they are all important themes.

these themes reflect the distinct sensibilities of both the modernist and postmodern aesthetic movements. (from google, you should paraphrase)

hope this !

- melanie