The length and width of a certain rectangle are both decreased by 50%. if the length and width of the new rectangle are then increased by 40%, the area of the resulting rectangle is what percent less than the area of the original rectangle?

51% less.

The length is decreased by 50%, which is the same as being multiplied by 0.5, then it's increased by 40% which is another multiplication by 1.4. So the overall change is 0.5 * 1.4 = 0.7, or the newest rectangle is 70% of the size of the original rectangle. And since the area increases by the square, the newest rectangle has 0.7 * 0.7 = 0.49 of the area as the original rectangle. So it has 51% less area than the original rectangle.