10 students went to both France and Spain. This means the intersection of the two circles has 10 people. Use this information to subtract 10 from the 20 that visited France and the 15 that visited Spain. There are then (20-10 = ) 10 people who went just to France and (15-10 = ) 5 people who went just to Spain. 10 + 5 + 10 is 25. 40 students were surveyed. 40-25 is 15. This means 15 people went to neither two countries