Question: There were 50 racers in a bicycle charity race at the beginning of the race. After 20 minutes, 30 more racers joined the race. The total number of racers doubled after another 30 minutes. If at the end of the race only 130 people finished the race, what's the total number of people who dropped before finishing the race? Think carefully first, then make a decision:
At the start, there were 50 racers, who were joined by 30 more racers, thus 50 + 30 = 80 racers. After 30 more minutes, the number of racers doubled, totaling 80 * 2 = 160 racers. If the number of racers who finished is 130, the 160 - 130 = 30 racers dropped before finishing. So the answer is 30.