Can i combine CL9 and CL10]?

Solution
No you should not mix memory types and speeds. Often even the exact same memory bought at different times has issues working together.

If you want to upgrade your memory, your only safe bet is to buy another pair of the EXACT SAME memory.

Rogue Leader

It's a trap!
Moderator
No you should not mix memory types and speeds. Often even the exact same memory bought at different times has issues working together.

If you want to upgrade your memory, your only safe bet is to buy another pair of the EXACT SAME memory.
 
Solution
Memory can sometimes be funny.

One of the main points is to make sure you get the same speed rating.
And the other is to check that the new memory kit works at the same voltage.

As for the memory timings, latency.
Most of the stated values have to be the same, the last value or its CL9 say to memory with CL10.
Can in some motherboards work fine where as with other motherboards it can create problems.

For a hassle free install you get the same brand of memory kit, and speed rating plus the correct latency timings as the existing two memory modules fitted to your system.