Unexpected result using floor() function

Hi all

 

I am running PostgreSQL 9.4.4 on Fedora 22.

 

SELECT floor(4.725 * 100 + 0.5) returns 473, which is what I expected.

 

SELECT floor(4.725 * power(10, 2) + 0.5) returns 472, which I find surprising.

 

Please can someone explain the anomaly.

 

Thanks

 

Frank Millman