Beach walk  math puzzle
Along the beach are a number of poles standing at equal distance from each other. The poles are numbered 1, 2, 3, 4, ..... Alice is walking from the first pole to the last one and back, Bob is doing that in the opposite direction. They start at the same time and walk with constant, but different velocity. Their first encounter is at pole number 10, their second (when they're both on the way back) at pole number 20. How many poles are standing along the beach? 

Grandfather's birthday  math puzzle
More than twenty years ago, Tim asked his grandfather who was celebrating his birthday that day: "How old are you now?" Grandfather smiled and said: "Add the digits of my year of birth and multiply the answer by 4." Tim would have looked so uncomfortable that his Grandfather immediately added, "By the way, this trick also works with the year we have on the calendar now." What was grandfathers age?