This is a puzzle I discovered very recently, and really enjoyed it. Here it goes:
There are 9 cards lying face up, with numbers 1-9 written on them. Ramesh and Mahesh start playing a game – they start picking up these cards alternately, without replacement. The first person to have exactly 3 cards that add up to 15 wins the game. Ramesh starts the game by picking the first card. Does Ramesh have a winning strategy?
Age Group: I think this should be feasible for 8+ years, though not an easy one.
Source: Picked this up from a book by the name “Mathematical Puzzles, a Connessieur’s Collection” by Peter Winkler