It took Leo 25 x 2 = <<25*2=50>>50 minutes to finish the second part of the assignment.
Leo finished the first and second parts of the assignment in 25 + 50 = <<25+50=75>>75 minutes.
He finished the entire assignment in 60 x 2 = <<60*2=120>>120 minutes.
Therefore, it took Leo 120 - 75 = <<120-75=45>>45 minutes to finish the third part of the assignment.
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