The perimeter (P) of a rectangle is calculated as:
P = 2 * (length + width)
In this case, the length of the garden is 35 meters, and the width is 25 meters:
P = 2 * (35 m + 25 m)
P = 2 * 60 m
P = 120 meters
Now, we need to calculate how many sets of posts are needed along this perimeter, given that the posts are set 5 meters apart. To do this, divide the perimeter by the distance between each set of posts:
Number of posts = Perimeter / Distance between posts
Number of posts = 120 m / 5 m/post
Number of posts = 24 posts
Andy will need 24 posts to build the fence around the rectangular garden.