Riddle: The pet shop starts with some dogs, then someone comes and takes 1 of the dogs, then another person and their child take 4 dogs. After that a mother, father and their 18 kids adopt 12 dogs. Then the pet shop receaves 3 dogs and someone takes 1, now the pet shop has 2 dogs. How many dogs did they have at the beginning?
Answer: 17 dogs because 17-1=16-4=12-12=0+3=3-1=2.