A National Highway Traffic Safety body is concerned about the fire hazards posed by vehicles involved in different types of collisions. They collate information of past accidents involving vehicle fires, including the type of car (electric vs petrol) and the type of collision (front collision vs rear collision). They construct the following contingency table from a random sample: Accident type Front Collision Rear Collision Type of vehicle Petrol 24 30 Electric 24 13 What is the total sample size? The next question uses information provided in this question. 12 pts