If you want to have the least wood, you must let it grow against the wall, then the length of wood = width ×2+ length, and you can solve it accordingly.

Solution: when the fence is long against the wall, the fence is the least?

8× 2+15 =16+15 = 31(pieces)

Answer: Use at least 3 1 piece of wood.

This is the knowledge that needs to be learned in the third grade of primary school. The third day, unit 3 content: "quadrilateral". This unit includes quadrilateral, parallelogram, perimeter, rectangle and square perimeter.

Perimeter of rectangle = (length+width) *2

Circumference of a square = either side *4

The perimeter of a triangle = the sum of three sides.