Tony will need to buy 22 fence posts in order to build a fence around his rectangular garden with dimensions 20 ft by 35 ft, with fence posts placed 5 ft apart. Hence, the correct answer is the option C)22.
To calculate the number of fence posts needed, we need to determine the perimeter of the rectangular garden and divide it by the spacing between the posts.
The perimeter of a rectangle is given by the formula: P = 2(l + w), where l is the length and w is the width.
In this case, the length is 20 ft and the width is 35 ft. Plugging these values into the formula, we get:
P = 2(20 + 35) = 2(55) = 110 ft.
Now, we need to divide the perimeter by the spacing between the posts, which is 5 ft.
Number of posts = Perimeter / Spacing = 110 ft / 5 ft = 22.