A rectangle has a perimeter of 18 units, and an area of 20 square units. What are the dimensions of the rectangle?
+21 We know a rectangle has two congruent pairs of sides.
So, we are trying to find what multiplies to 20 and adds to 9 (half of 18 because we are only counting one pair).
x*y = 20
x + y = 9
The factors of 20 are 1,2,4,5,10,20 and two of those add up to 9.
When we look carefully we find those two are 4 and 5.
Sooo the dimensions of the rectangle are 4 and 5.
(Tell me if anything is wrong here) 
