The length of the rectangle is 8 cm. This is 2/5 of its perimeter. What is the width of the rectangle?

We find from what number 8 cm is 2/5.
Since two parts are 8 cm, one part is equal to 4.
Parts 5, which means the number is:
4 x 5 = 20 cm.
We get that the perimeter is 20 cm.
Since in a rectangle the opposite sides are equal, and one of them is 8 cm,
Then the other side remains:
20- (8 + 8) = 4 cm.
4: 2 = 2 cm.
Answer: the width is 2 cm.