gistfile1.txt

caseCount = int(input())


def compute_sum(num):
    result = 0
    for o in str(num):
        o = int(o)
        result += o
    return str(result)


for i in range(caseCount):
    lines = int(input())
    res = 0
    for j in range(lines):
        l = input()
        x = int(l.split(' ')[0])
        y = int(l.split(' ')[1])
        res += x * y
    while len(str(res)) > 1:
        res = compute_sum(res)
    print(res)