Question Ram detected but not registered

[Ryanl4k]

So I recently purchased two 8gb ram stick one was a crucial cl17 2400mhz and the other was the same but one was labelled 1745 MT and the other 1733 SU, when I put both in the ram slots, only the MT was registered but when I opened task manager there registered 16 GB but only one 8gb was being used, I'm new to pc building so I'm not so familiar with this luulz

 

[Calvin7]

Memory is guaranteed in the form sold. Other combinations you decide to make have no guarantee to be compatible together.