Did you know Lexmark now has twin packs for some of their inks? If you use one of the following printers:
X74
X75
X1140
X1150
X1170
X1185
X2250
Z13
Z23
Z25
Z33
Z35
Z513
Z515
Z603
Z605
Z615
you can buy either a normal use black ink (10N0016) twin pack, moderate use black ink (10N0217) twin pack, a twin pack with a black and a colour (10N0217 & 10N0227) , or a colour ink (10N0227) twin pack.
If you have one of these:
Z55
Z55se
Z65
Z65N
X5150
X6150
X6170
you can buy either a black ink (18L0032) twin pack or a twin pack with a black and a colour (18L0032 & 118L0042).
These twin packs work out way cheaper than buying the cartridges singly, and if you know you are going to use them within, say, a year, you will be saving yourself money and time.