Every 10 seconds, there is a car collision, and every 20 seconds there is a big crash. How many accidents overall will happen in 4 minutes? Let's be accurate as possible.
1 minute is 60 seconds, so 4 minutes is 4 * 60 = 240 seconds. During this time there would be 240 / 20 = 12 big crashes. And also 240 / 10 = 24 car collisions. So in total during 4 minutes there would be 12 + 24 = 36 accidents.
The answer: 36.