Imagine the other team scored 0. Rangers could have scored 0,1,2,3,4, or5. Imagine the other team scored 1. Rangers could have scored 0,1,2,3 or 4, Imagine the other team scored 2. Rangers could have scored 0,1,2 or 3 The other team could not have scored 3, or they would have won. So you are adding 6+5+4. This is a section from triangular numbers. Triangular numbers just mean: 1, 1+2, 1+2+3 and so on until you get to in this case 1+2+3+4+5+6. So you could use the formula for adding triangular numbers to 6 then use the formula again to subtract the triangular numbers to 3. This is a long winded way of saying: yes, there is a formula, but in this case it is more trouble than it is worth and way beyond 11+. (The formula for triangular numbers is n(n+1)/2, where n is the number of numbers you are adding)
