Find by name and mtime

Hi,
I'm trying to find all files that have a .ksh and .p extension and that are 7 days old by using the below find command but it doesn't seem to as expected. It gives me random results.. Can someone point out what may be wrong?

find . -name "*.ksh" -o -name "*.p" -mtime -7 

$ find . \( -name "*.ksh" -o -name "*.p" \) -mtime -7

Thanks for the quick response.. That seems to of done the trick...