101Leafy researched the games.
Book of Combos 5
Pro text. Along with 1, 2, 3 and 4, improves your combining success rate.
Adds 45% to all Item Combination success ratios. Must own Book of Combos 1, 2, 3 and 4.
BradyGames, Monster Hunter Official Strategy Guide, 2004, p. 73