there are 68 runners in a marathon . 28 runners finish the race. Then 22 more runners finish the race .how many runners have not finished the race ?
To find out how many runners have not finished the race, we need to subtract the number of runners who finished from the total number of runners:
Total number of runners - Number of runners who finished = Number of runners who have not finished
68 runners - 28 runners = 40 runners who have not finished the race
Since 22 more runners finished the race, we need to subtract this additional number from the total number of runners who have not finished:
40 runners - 22 runners = <<40-22=18>>18 runners who have not finished the race. Answer: \boxed{18}.