The half-life of a radioactive kind of protactinium is 27 days. How much will be left after 54 days, if you start with 488 grams of it?
grams
After 27 days, half of the protactinium will decay, leaving 244 grams. After another 27 days (54 days total), half of the remaining protactinium will decay, leaving 122 grams.
Therefore, after 54 days, if you start with 488 grams of protactinium, there will be 122 grams left.