The half-life of a radioactive kind of nitrogen is 10 minutes. If you start with 120 grams of it, how much will be left after 20 minutes?
The half-life of a radioactive substance is the time it takes for half of the substance to decay. In this case, the half-life of nitrogen is 10 minutes.
After 10 minutes, half of the original amount of nitrogen will remain. So, after the first 10 minutes, there will be 120 grams / 2 = <<120/2=60>>60 grams of nitrogen left.
After another 10 minutes (a total of 20 minutes), there will be another half-life. So, half of the 60 grams remaining will decay, leaving 60 grams / 2 = <<60/2=30>>30 grams of nitrogen.
Therefore, after 20 minutes, 30 grams of nitrogen will be left.