From the last sentence of the intro: "At the rate of 20 to 50 total Mars trips, it will take anywhere from 40 to 100 years to achieve a fully self-sustaining civilization with one million people on Mars."
What Musk actually said was that, with 100 people per vehicle, it would take 10,000 vehicle trips to move the 1 million people to Mars. Since Mars and Earth are in the proper launch window about every 2 years, there would be 20 to 50 launch windows in the 40-100 year period he is modeling. If you want to do 10,000 vehicle trips in 20 windows (40 years) you would need an average of 500 vehicles, all launching at roughly the same time at each launch window (this explains Musk's reference to the video sequence from Battlestar Galactica when all the shipsgo to light speed at once). If you had more vehicles or more passengers per vehicle, it could be done in fewer launch windows. The math is obvious but the intro seems to make it as confusing as possible.