Problem solving Q about number of houses in a street.

Question

A row is marked with 1,2,3,4....

The marking continues down the other side - the largest mark opposite is 1.

Each mark has another directly opposite it.

If mark 17 is opposite number 56, how many marks are there in the row?

Answer 1

If the largest number is $N$, what is the sum of the house numbers of house $1$ and the one opposite to it? What is the sum of the house numbers of house $2$ and the one opposite to it?

Answer 2

Brute force is an entirely acceptable way to solve this problem. If 17 is opposite 56, then 16 is opposite 57, 15 is opposite 58, and so on. Keep going. Which house is then opposite 1?