Lovely will sell 10 x 2/5 = <<10*2/5=4>>4 books for $2.50 each.
She will sell 10 - 4 = <<10-4=6>>6 books for $2 each.
Her earnings for the 4 books at $2.50 will be $2.50 x 4 = $<<2.5*4=10>>10.
Her earnings for the 6 books for $2 each will be $2 x 6 = $<<2*6=12>>12.
Thus, Lovely's total earning if all 10 books are sold is $10 + $12 = $22.
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