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.