18. 
Cover an area of 45 squares in a 5 by 9 rectangle. 
19. 
Fill a rectangle of area 50 squares.

20. 
Fill a rectangle of area 55 squares.


Using all 12 pentominoes to fill a rectangle can be done in 3 different ways.
As a 3 by 20 rectangle; as a 5 by 12 rectangle; as a 6 by 10 rectangle.
The 3 by 20 was done in problem #16 (above).
One solution to the 5 by 12 (from among several thousand) is shown below.



21. 
Find a different way to fill the 5 by 12 rectangle. 
22. 
Use the full set of 12 pentominoes to fill a 6 by 10 rectangle. 