00:01
To determine when f of t will be equal to 50%, we just let f of t equal 0 .5.
00:07
So 0 .5 is equal to 1 minus e to the negative 0 .1t.
00:11
We can add this, sorry, this is negative 0 .15t.
00:16
We can add this e over to the other side.
00:20
So we get 0 .5 plus e to the negative 0 .15t.
00:24
It's equal to 1.
00:26
You can minus this 0 .15 over.
00:28
We get e to the negative.
00:30
0 .15t is equal to 0 .5.
00:34
We take the natural log of both sides and we can bring down the exponent.
00:38
So we have negative .15t times the natural log of e is equal to the natural log of 0 .5.
00:44
And the natural log of e is just 1.
00:47
So we have now negative .15t is equal to the natural log of 0 .5.
00:52
We divide by both sides by negative .15 and we get t is equal to the natural log of 0 .5, divided by negative 0 .15...