The video at http://tinyurl.com/lzy6gt offers a math challenge for evolution. It comes from Carl Baugh and a math "professor" (actually a high school and trade school math teacher). The math teacher calculates that evolution can't be true because it would mean that there would be too many people on Earth.
The math teacher uses the formula for compound interest that you would use for a bank account.
If you start with $100 and have a 5% interest rate, in a year you'll have $105. Then if you wait another year you'll have 1.05 times $105 or $110.25. That extra $0.25 is the interest on the $5 you earned last year. It adds up.
You can use the math teacher's formula to figure out how much money you will have after any number of years.
Is there anything wrong with that?
Probably the most obvious problem is that the formula for compound interest works only if you leave the money in the bank. If you took $5 out of the bank account after the first year, you wouldn't have $110.25 after the second year. You'd only have $105 again.
With bank accounts, that's OK.
But it's not OK for people. That's because people die.
The calculation assumes that people live forever and continue to reproduce at the same rate forever. It requires, for example, that Noah and his family are still reproducing somewhere.
I don't have any great-great-great-great...grandparents who are still alive and having children.
There are many other problems with the assumptions used for the formula. For example it ignores things like plagues, wars and other disasters that actually cause human population totals to diminish. Also, censuses that we do have from ancient times show that current population growth rates are MUCH higher now that they were in the past. The main impetus for the current population growth rates was the Industrial Revolution. So when Baugh and his math teacher claim that they are being generous with their estimated growth rate of 0.456%, that's untrue.
Finally, their assumptions allow them to begin with eight people after the flood and come up with the current population of 6.5 billion people now. Those are the end points and the math works for those points.
But if the math is correct, it should also match population totals at intermediate dates.
It doesn't. It's wrong at every step
For example, the Census of Qurinius mentioned in the Book of Luke, showed that there were 4 million Roman citizens living within the Roman Empire. (See http://www.askelm.com/star/star014.htm)
Obviously that doesn't include any non-Roman citizens living within the empire (such as Mary and Joseph). Neither does it include anyone living outside of the Empire such as in the Western Hemisphere, Australia, China, etc.
Yet the formula comes up with only 35,000 people in the ENTIRE world! That's off by many orders of magnitude! (The estimated world human population was 200 million at that time,)
The math, along with the many false assumptions, would be laughed at by anyone who had completed junior high school.
But it impresses creationists.
As a side note, actually far and away the biggest problem for growth rate calculations is that for the vast majority of human history, we were hunter-gatherers.
That fact means that we were nomadic. We would move from place-to-place in bands of 30 individuals or less, eat the grains and fruits and hunt the game found in that place and then move on.
There are problems with that life style if you have a significant growth rate.
For one thing, if the growth rate is large you can't migrate effectively with numerous small children. At MOST you could only have two children that couldn't walk long distances on their own.
The second problem is that if the population grows quickly then you can't stay in one place as long because the available food is used up more quickly in that single place.
That means that you have to move more often and find more places to live in over a year.
Inevitably you will run into other bands of hunter-gatherers who are using or would like to use these new places with available food. Inevitably conflicts will break out which will diminish the population.
The bottom line, hunter-gatherer societies reach a stable population and can't really grow at all past that point. So the effective human population growth for most of human history was, effectively, ZERO.
Another, possibly more obvious flaw, comes if we decide to use reproductions rates of other species. For example, some bacteria can reproduce every 15 minutes. They can double their population 96 times in a single day. Using the mathematics of Carl Baugh’s math professor the entire universe would be infested with bacteria within a week! Since that isn’t the case the Earth can’t be more than a day or two old.
Because of all of those reasons, human population growth rates can’t be use to calculate the age of the Earth.
 http://www.census.gov/ipc/www/worldhis.html, shows population estimates from the US Census Bureau, referenced on September 2, 2009