Question 5: how long will it take for 2 g of a sample of iodine-131, which has a half-life of about 8 days, to decay to 0.04 g?

This problem can be represented through the following equation

A = A₀(1/2)^t/h

where

A>  is the amount of substance left after time t

A₀ > is the original amount> 2 g

h>  is the half-life> 8 days

for A=0.04 g

t=?

0.04 = 2(1/2)^t/8

0.02 = (1/2)^t/8

Take ln on both sides:

ln(0.02) = ln [(1/2)^t/8]

ln(0.02) = (t/8)(ln 1/2)

t = 8*ln(0.02)/ln(1/2)

t = 45.15 days

the answer is 45.15 days

341

step-by-step explanation:

all you have to do is 9x31 (which equals 279) and then 20x31 (which equals 620). then you have to subtract. 620-279=341.

7.25

step-by-step explanation:

we know that 7 equals to 7.0. we also know that 1/4=0.25. so we can add the two together and we get 7.25