a peculiar result with Google (but not so unusual)

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At www.google.com I did a search for "dentist qualifications" (w/o the
quotes) and I got 624,000 hits.  Then I added the word   "check" (again
w/o quotes)--and I got 1,250,000 hits!  I should have gotten *fewer*
hits, not more, since search arguments are (in my understanding) ANDed.

This is not the first time this sort of thing has occurred.
Can anyone help me understand what's going on?

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