Trouble writing to external hard drive on macbook pro.
I just bought a used macbook pro and i am trying to write files to my external hard drive from the macbook and i only have read only permissions. I have an iMac that i used the hard drives on and have read & write permissions on it. I am able to use the hard drives on pc as well with no issues but on any other mac i only have read only permissions. The drives were setup to use on both pc and mac when first formatted. I also cannot change the permissions on my iMac as there is no gold lock in the corner. Anybody else had this problem? Thanks
2011 iMac
20gb ram
500gb hard drive
quad core i5
2011 Macbook Pro
4gb ram
500gb hard drive
quad core i7
MacBook Pro, OS X Yosemite (10.10.2)