Trying to install Ubuntu Mate 15.10

[Glenn / Lenny]

Hi,
I left about 40 GB as free space on my HD to install Ubuntu along side Windows.
I am using Orca.
I am in the partitioning section, and I select the free space, and it calls it /dev/sda5, and it will allow me to either set the file system area, mounted at /, or swap.
When I select one, it removes the other.
This is frustrating, why cannot I just tell it free space and have it create the swap area?
This is touchy because I don't want to destroy /dev/sda1.
Thanks for any assistance.
Glenn
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