Two crews were assigned the job of setting 900 fence posts. By the time the job was completed, one crew had set only 7/8 as many fence posts as the other crew. How many fence posts were set by the faster group?

Answer 1

If the faster group set x posts, then
x + 7/8 x = 900

Or, if the faster group set 8n posts, then the slower group set 7n posts.
8n + 7n = 900