standard_description: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
problem_activity: Problem 1
a.   Create as many rectangles as you can with an area of 12 square units. Find the perimeter of each rectangle that you created. Then record the length, width, area, and perimeter of each rectangle in the table below:
| **                Length (units)               ** | **                Width (units)               ** | **                Area (square units)               ** | **                Perimeter (units)               ** |
|---------------------------------------------------|--------------------------------------------------|--------------------------------------------------------|------------------------------------------------------|
|                                                   |                                                  |                                                        |                                                      |
|                                                   |                                                  |                                                        |                                                      |
|                                                   |                                                  |                                                        |                                                      |
|                                                   |                                                  |                                                        |                                                      |
|                                                   |                                                  |                                                        |                                                      |
|                                                   |                                                  |                                                        |                                                      |
|                                                   |                                                  |                                                        |                                                      |
b.   What do you notice about the rectangles you created? What do you wonder?
Problem 2
What is the greatest perimeter you can make with a rectangle that has an area of 24 square units?


aligns: no