Floating point or decimal numbers are not currently supported in the JS Blocks Editor, just integers.

You can however, multiply all numbers by 100 to do the computation, and then display separate whole and fractional parts when you display them. 

If you want to make use of floating point arithmetic, you could move to MicroPython as that supports them.

The alpha version of Makecode now supports floating point numbers. Try it out and feed back to us. Remember it is a pre-release so may have some bugs!