b How much of the sample in mg remains after 20 years After 20 years we have the following Round your final answer to two decimal places y 20 Step 6 50 2 31 50 t 30 2 3 c After how many years will only 1 mg remain 2 3 To find the time at which only 1 mg remains we must solve 1 y t 50 2 t 30 and so we get the following t 30 log 1 50 1 50 In 31 50 mg Step 7 Hence we conclude the following Round your final answer to one decimal place In 2