i realize Swift is now 3.1 and the book was written prior to this update, but could you please explain why inferred types do this. note: if you specify the type, you get a correct return.
Also, if the value would be 91.2 you also get a correct return. This does not occur for every value ending in “xx.1” begins at 71.1 and seems to end after 91.1 . Does swift have something against these particular radio stations 
Ask yourself: How can I encode 0.1 in binary, in a finite number of bits?
0.5, 0.25 and 0.125 are easy, but 0.1 is a challenge.