A camping site recorded a total of 150 campers for the past three weeks. Two weeks ago, there were 40 campers which was 10 more than the number of campers three weeks ago. How many campers were there last week? Think carefully first, then make a decision:
Three weeks ago, there were 40 - 10 = 30 campers. The total number of campers from three to two weeks ago is 30 + 40 = 70. Hence, there were 150 - 70 = 80 campers last week. So, the answer is 80.