AHi, I just baked four sheet cakes (11X15X2) One of the cakes cracked, from one end to the other. I really don't want to bake another cake so I'm trying to salvage this one. I'm creating a number birthday cake, 27. It will be a four layer cake with buttercream filling, covered in fondant.

Even thou the cake is cracked, will I still be able to cut it into a number ( 2 or 7)? Can I use buttercream to repair this or will I have to bake another sheet cake?

Please help, as I need to finish this cake by Friday morning. Thanks :(

I don't see why not, I have patched broken cakes with no problem, just put some ganache or buttercream on the break, and stick em together.

What kind of cake?  If its very tender (i.e. white vanilla cake) and prone to crumbling it will be trickier.  I say before trying to carve the numbers you glue this crack back together.  I'm assuming you already removed the cake from the pan.  Lay down a large sheet of plastic wrap down on a cookie sheet first and gently place the cracked cake on top.  Use a cake flipper or several large spatulas if you have them.  Go ahead and pipe whatever frosting you'll be using inside the crack and adhere the fracture back together.  Now use the plastic wrap as a bandage and wrap the cake up tightly but still keeping it in the shape.  Use additional plastic wrap to cover the entire cake and then a layer of tinfoil on top of that.  Pop the cake (still resting on the pan for support) in your freezer and let it firm up.  This will probably take at least 30 minutes.  I do this normally to all my cakes.  I bake them ahead of time; cool; wrap in plastic then tinfoil; and freeze for days/weeks.  Just note - you are wrapping up the naked cake...not the cake and the pan together.  

Chilled cakes are much easier to work with and carve.  If you let it sit in the freezer more than 1-2 hours you will need to let it come back up to temperature a lil,  You don't want to try to cut/carve a cake that's frozen solid.  Just get it to a firm chilled state.

Good luck!!