How to do half lives:
Let's say you are given 64 grams of something with a half life of 7 days. This means every 7 days, half of what you started with goes away.
If they ask you how much is left after 21 days, you first divide 21 by 7 to get "n" the number of half lives: 3
Then you set up your calculator like this:
Amount = Starting amount (0.5)^n
Best way is to do this from right to left (backwards)
so,
Enter 0.5
hit the xY key (just below m+)
enter n (3 in this case)
press equals
multiply all of this by your starting amount (64)
you should get 16 grams left
Try this with 128 grams and a half life of 6 days, after 42 days
You should get 18/6 = 3 = n
0.5 xy 7 = 0.125
128 x 0.125 = 16 grams
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