00:01
Alright, they give us an equation for this function a of t equals 291 e to the negative .044 t.
00:13
And they tell us that they want to know how much of this substance exists after 130 years.
00:21
So you just plug in 130 for t.
00:28
And you punch that right in your calculator, 291 e to the negative 0 .044 times 130.
00:37
And that comes out to be .954 and a whole bunch of other stuff.
00:42
They want you to round to one decimal place.
00:45
So this 5 makes that 9 to 10.
00:48
So that makes that 1 .0 grams.
00:53
Alright, then the second question wants to know what is its half -life.
00:57
So if the initial amount of this substance is 291, half of that is 145 .5.
01:11
So i'll divide each side by 291 and of course get .5 equals e to the negative .044 t...