RAID 1 - Speed with diferent speed disks

I was wondering...

I have a RAID 1 with an SDD and a HDD disk.

Of course, the Write speed should be the same as the HDD disk.

But the read speed? The SDD disk is called more times than de HDD? Or RAID1 call exactly 50% of the content on each disk?

Sorry if my english is not enough. Just ask if you don't understand me. Bye ;)