The answer are below, the work is show step by step.
There will be a 25 grams left after 3240 years.
The half-life of Radium-226 is 1620 years. If we divide 3240 by 1620 the answer is 2. So that means the amount of Radium-226 will divide in half twice.
100 / 2 = 50 / 2 = 25
1.67 cups.
10 divided by 6, then round.
10x20x2=$400
All you have to do is find the area of the floor(10x20=200),then you just multiple the area by the cost(200x$2=$400),and that is how you find the cost.