Hello from MrBillDoesMath!
Answer:
The first marker is labeled 208708; the second (consecutive) one 208709
Discussion:
Call the first mile marker "m". Then
m + (m+1) = 417417 => combine like terms
2m + 1 = 417417 => subtract 1 from both sides
2m = 417416 => divide both sides by 2
m = 417416/2 = 208708
Note: m and (m+1) are consecutive as they immediately follow each other in the set of integers.
Thank you,
MrB
