Well not all lines are lines of symmerty, because if you draw a let's say a rectangle on a piece of paper and draw a diagonal line through it, well the two sides don't really lie perfectly on one another!!
So in 5 weeks, Marcie will have collected 25 stickers, and given away 15. She will have 10 stickers left. I hope that this helps! :)
The numbers are 1 and 2
1 squared = 1 because 1 x 1 = 1
2 squared = 4 because 2 x 2 = 4
4 - 1 = 3
I think that using the elimination method is the best, because it is the only method that I use when solving these types of equation. For example, for these two equations, you need to multiply one of the equations by a certain number so that you'd be able to find x and y. The elimination method is the method that tells you to do that. It is also the easiest method.
~Hope I helped!~