问答题A set dominoes(多米诺) consists of rectangular (矩形的) tiles each carrying two numbers from 0 to 6 which represented by patterns of spots. Every possible pairing of numbers occurs just once including each number with itself. How many dominoes are there in
题目
问答题
A set dominoes(多米诺) consists of rectangular (矩形的) tiles each carrying two numbers from 0 to 6 which represented by patterns of spots. Every possible pairing of numbers occurs just once including each number with itself. How many dominoes are there in a set?