The bridge below has been painted in a black-and-white checkerboard pattern.
Starting at the bottom-left arrow, you need to cross the bridge and finish at the upper-right arrow. You can move one square at a time, either up, down, left, or right. You can't move diagonally.
Now here's the tricky part: how many different routes across are there that touch exactly four black squares and three white squares?
UK Version
The bridge below has been painted in a black-and-white check pattern.
Starting from the bottom-left arrow, you need to cross the bridge and finish at the top-right arrow. You can move one square at a time, either up, down, left or right. You can't move diagonally.
Now here's the tricky part: how many different routes across are there that cross exactly four black squares and three white squares?