1998 CEMC Gauss (Grade 7) Problems/Problem 7

Problem

A rectangular field is 80 m long and 60 m wide. If fence posts are placed at the corners and are 10 m apart along the 4 sides of the field, how many posts are needed to completely fence the field?

$\text{(A)}\ 24 \qquad \text{(B)}\ 26 \qquad \text{(C)}\ 28 \qquad \text{(D)}\ 30 \qquad \text{(E)}\ 32$

Solution

There is one post on each of the corners, along with 7 other posts along each of the two lengths and 5 other posts along each of the two widths. In total, this gives us $\boxed{\textbf{(C)}\ 28}$ posts.