21 = 2
22 = 4
23 = 8
24 = 16
25 = 32
26 = 64
27 = 128
28 = 256
29 = 512
210 = 1024
211 = 2048
212 = 4096
213 = 8192
214 = 16384
215 = 32768
216 = 65536
As you can see the units digits go 2,4,8,6,2,4,8,6,...
Every time the exponent to which 2 is raised is a
multiple of 4, the units digit is a 6.
Therefore since 4000 is a multiple of 4,
24000 has units digit 6.
Edwin
