23) Your friend says that the flood in 2010 was a 100-year flood and the flood in 2009 was a 200-year flood so it will be at least 300 years before we see another flood like them. Is your friend correct?

My friend is incorrect. It will take another 200 years for a flood of that sort to occur again

Explanation:

The said friend mentioned that the flood in 2010 was a 100-year flood; This indicates it lasted from 1910 to 2010 which gives a 100 years

Then in 2009, the flood lasted for 200 years which indicates the flood had just a year difference between that of 2010 and that of 2009. Jointly, the floods lasted 200 years with just a year difference if analyzing between 2009 and 2010.

Therefore, It will take another 200 years for a flood of that sort to occur again with of course, a year difference in interval between that of 2009 and 2010