Problem number four. Five baby kangaroos are hopping to their mothers along the paths shown below. Which path is the shortest? So we need to count the lengths of the red lines in each of the pictures and see which of them is the shortest. Notice that the red line is divided into horizontal parts that go left and right and vertical parts that go up and down. For example, in the first picture, we have marked the three vertical parts in blue, and you can count that there are ten horizontal and three vertical parts. Similarly, in B, we've marked the vertical parts in blue, and you can count that there are ten horizontal and five vertical parts. Since the vertical and horizontal parts have the same length, this means that A is shorter than B, because it has the same amount of horizontal parts, but less vertical distance. Similarly, we can do the same logic for C, D, and E, and you can see that C has ten horizontal and eight vertical, D has ten horizontal and four vertical, and E has ten horizontal and eight vertical. The horizontal distance is the same, because the kangaroo is always hopping towards the mother, but the vertical distance changes because in each picture, the amount the kangaroo goes up and down is different. We can see that in A, the total vertical distance is three, which is smaller than any of the other vertical distances. Therefore, the answer is A.

shortest path

baby kangaroos

vertical segments

path A

quickest route