There are over 70 challenges in the game. To be more precise they are challenge sets, with each set having 1-3 smaller challenges to complete. There are plenty of easy challenges in the bunch that you'll knock out without even trying, so you're sure to get this while heading towards the plat, if not by the end of the story like I did. You also need to complete 46 challenges for Jack of All Trades so this will come on the way to that.