00:02
So we are going to use the population growth model where a is equal to a sub -0, which is the initial population, times 2 to the power of t divided by d, where d is doubling time.
00:17
And so now we know that a -7 -0 is equal to 2 ,200 because it is given, and we also know that the doubling time is 2.
00:27
And so if we substitute in these known values into our model, we get that a is equal to 2 ,200 times 2 to the power of t divided by 2.
00:39
And so this is the exponential equation for population a at time t.
00:46
And so for part a, we want to see the number of transistors in the year 1990.
00:55
And so because t equals zero corresponds to the year in 1970, that means t equals 20 in the year 1990.
01:07
So for part a, t is going to equal 20.
01:10
And so we substitute in t equals 20 into our model that we just wrote up here.
01:16
And so a is going to be equal to 2 ,200 times 2 to the power of 20 over 2...