F10, F11, F12 work as function keys, not volume
After upgrading to El Capitan my iMac Bluetooth keyboard has changed from the F10, F11, F12 keys operating the volume to now being function key shortcuts to Mission Control. I've found a few articles that show in System Preferences how to un-select them from being function keys in the Mission Control and Keyboard areas but that doesn't fix my problem.
How do I change it back so these keys operate the volume?
iMac (21.5-inch Mid 2011), OS X El Capitan (10.11)