Four $5 bills amount to $5 x 4 = $<<5*4=20>>20.
Three $20 bills amount to $20 x 3 = $<<20*3=60>>60.
So Gail's $5 and $20 bills amount to $20 + $60 = $80.
Thus, her $10 bills amount to $100 - $80 = $20.
Therefore, she has $20/$10 = <<20/10=2>>2 $10 bills.
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