After the first day, Ezekiel had 50 - 10 = <<50-10=40>>40 kilometers of the hike left.
On the second day, he covered 50 / 2 = <<50/2=25>>25 kilometers.
Therefore, on the third day, he had 40 - 25 = <<40-25=15>>15 kilometers left to finish the hike.
#### 15