1. The problem statement, all variables and given/known data This is the equation y = y0e-kt 2. Relevant equations b) Show using your expression for λ that if at time t1 the amount is y1, then at time t1 + λ it will be y1/2, no matter what t1 is. 3. The attempt at a solution y1=y0ekt1 that part I got. Then the answer key goes into the next step saying:λ = (−ln2/k)y0ek(t1+λ) That is where I got lost. What is the step to go from the y1 equation into the lambda equation? I know that for half life, y1=y0/2 so that makes t=ln2/k . The time it takes for an element to decompose to half its mass is t=ln2/k . How do I make the connection to the very last lambda equation?