not 100% sure about the provided solution for this one because of a few things, details in spoiler below!
First of all: the "Country" column in the solution includes some interesting data points like "Greece-1" for "Sofia Marinou". On closer inspection - Events that have a -1 or a -2 appended to the Country name are team events : Tennis and Skating. My solution removes the appended -1, -2 and -3 from the Country name to as to avoid double-counting the participation chart.
There's some interesting results in the Figure Skating in the 1908 Summer Games in London - Great Britain took home all of the Gold, Silver and Bronze medals. Does that mean that GB fielded three teams in Figure Skating?
Anyway - I don't get the EXACT same count as the solution, but I get roughly something similar.
Not to be picky, but I think a few people have pointed out the supplied output doesn't appear to be correct. Looking at women participation, it says: find the number of female athletes that participated in each game. The participants table contains the listing for athletes' participation in each event. The output is counting some athletes more than once. For example, Marion Jones participated in the 1900 Olympics in Tennis and appears twice - she completed in singles and mixed doubles. She's being counted twice in the results so that in 1900 is shows 33 athletes participating. I believe it was 23 athletes competing. (Though Google says it was 22. Not sure if i have a dup somewhere).