Identify the initial amount
Identify the half-life value
Divide the elapsed time by the half-life
Find how many half-lives have passed
Repeatedly halve the amount for each half-life
Use the formula: remaining amount = initial amount × (1/2)^(elapsed time ÷ half-life)
Solve for time if needed using: time = half-life × log2(initial amount ÷ remaining amount)