Cristian was installing a fence with his Dad on all four sides of a backyard. The yard is 40 feet long and 50 feet wide. Two-fifths of the fence will be chain link. How many feet of chain link will him and his Dad need?

72 feet

Step-by-step explanation:

We first need to find the perimeter of yard, then, we find 2/5 of the perimeter to find the length of chain link that they will need.

The yard is rectangular and it has dimensions 40 feet long and 50 feet wide.

The perimeter of a rectangle is given as:

P = 2 (L + W)

where L = length

W = width

Therefore, the perimeter of the yard is:

P = 2 (40 + 50)

P = 2 (90) = 180 feet

The length of chain link that they will need is therefore:

2/5 * 180 = 72 feet

They need 72 feet of chain link.