Will a 1600MHz RAM work with a 1333 MHz one?

[lebin]

If both modules have 9 latency and 1.5V, will it work together?

 

[middlemarkal]

yes but it will slow down to 1333

 

[geofelt]

Ram is sold in kits for a reason.
A motherboard must manage all the ram using the same specs of voltage, cas and speed.
Ram from the same vendor and part number can be made up of differing manufacturing components over time.
Some motherboards can be very sensitive to this.
That is why ram vendors will NOT support ram that is not bought in one kit.

If you can get it to work at all, speed will be limited to 1333.

If you own both, try it.
If you are looking to buy, buy a 2 stick kit of the capacity you need and keep the single stick as a spare.