Pontoon card game

Today we played a version of the card game Pontoon. We picked 3 cards and added them up, aiming for a total of 20. Then we decided if we should stick or twist, depending on how close we were to 20.  Some of us were bust straight away!  Some of us were very close to 20, but then chose another card and got more than 20!  We are working on strategies to help us...