Great Idea!
I like the idea behind this game, but it needs a little more of a challenge. If you really want to make a great game, try putting in some penalties. If you get the pair wrong, then subtract points. Also maybe keep the time limit the same throughout the entire game. This will make this game harder to beat. Maybe even add achievements for players to earn as they progress through the levels. But all in all, good game. Thanks very much more the brain exercise.