This article is from the Macintosh hardware FAQ, by Elliotte Rusty Harold email@example.com with numerous contributions by others.
All 68020 and 68030 desktop Macs that did not ship with an FPU standard
(i.e. the IIsi and LC series) have special slots that can accommodate
an FPU card. All Macs that have the FPUless 680LC40 CPU run just
fine if that chip is replaced with a full 68040 that includes an FPU.
All PowerPC Macs include an integrated FPU. There is no way to add
only an FPU to a 68000 Mac like an SE though some third party
accelerators do include FPU's as well as faster CPU's.