find command doesn't accept different unit of measurement with -and operator

When I issue: find / ( -type f -size 10M ) -and ( -type f -size 1G )
don't receive any answer; however, when I type:
find / ( -type f -size 10M ) -and ( -type f -size 1000M )
bash retu a few files.
What's wrong?
Can't I use different unit of measurement in both sides of the operator -and? (I apologize about my awful English)