Calculating Half-Life of Radioactive KCl

[abrowaqas]

Homework Statement

2.71g sample of radioactive KCl is decaying at a constant rate of 400Bq into the isotope 40K. which constitutes 1.17% of normal K. calculate the half life of this nuclide.

Homework Equations

we have dn/dt = n * lamda and t-1/2 = 0.693/lamda.

The Attempt at a Solution

how i put the value of N... which is not clear in question

 

[6Stang7]

You have a differential equation, so you need to find your boundary conditions