How many different rectangles can you make with aperimeter of 12 matchstick

2 answers

Assuming that it is a square with three matchsticks on each side, matchsticks can be added internally to give nine squares with each side of one matchstick.
you need length+width=6, so
1x5
2x4
3x3

If you were angling for the more complex scenario proposed by PsyDAG, then things do get a bit trickier.