My task was to find (using R) in which year the maximum number of children were born (http://www.openintro.org/stat/data/present.R). First thing I did, I added up the boys and girls values and found a summary, where maximum was 4268000. But it didn't work for me when it came to subsetting, so I just found summary for boys and girls separately and applied subset() twice to check if it is the same year. Well, I was lucky this time, in both cases the year was 1961. But the thing is that the total of the two maximum figures was 4268326. So my question is: why are they different?

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