Question 27
A neighbourhood survey finds 40 households with a Nguyễn, 41 with a Trịnh and 48 with a Lê. There are 22 with both Nguyễn and Trịnh, 20 with Trịnh and Lê, 25 with Nguyễn and Lê, and 10 with all three. Six households have none of these surnames. How many households are there altogether?
