The area of a rectangle is 20 cm² after its dimensions were doubled. What is the area of the original parallelogram?

If the original length and breadth of the rectangle/parallelogram was L and B respectively, then

Original Area = L*B

Once the dimensions are doubled, the length and breadth are now 2L and 2B respectively, so

New Area = 2L*2B = 4LB

New Area/Original Area = 4LB/LB = 4.

So, the new area is 4 times bigger. Therefore the original area is one fourth of 20cm², which is 5cm².