There are 41 blades in the picture of the pattern shown. If one were dividing/ drawing a circle into 9 degree increments, yes that number of blades is 40. But quilt math is not the same as real math because you are sewing all those pieces together and losing the equivalent of one whole blade with all the seam allowances. Don't worry about the angle. Just like only in 'quilting math' does 2.5 + 2.5 equal to 4.5. (Take a 2.5" square, sew to another 2.5" square, and you will not get a 5" square as a result.)