The manual specifies either single modules or matched pairs -- there is no listed configuration for mismatched modules. [URL]  
I have upgraded the ram with 1 Crusial 16 GB 3200 Mhz - CT16G4SFRA32A. Laptop model : G5SE 5505 Previously had, 2 x4GB .Now the laptop is detecting only 1 ram placed in slot 2 when 16 GB and 4 GB is being placed together. When both the 4 GB ram are placed together, both are getting detected. All the 3 ram (1x 16 GB and 2 x4GB ) are of 3200Mhz. Is there any option to use 20GB ram or is it not possible at all ? 
G5SE 5505 16 GB + 4 GB ram not working