standard_description: Prove that, given a system of two equations in two variables, replacing one equation by the sum of that equation and a multiple of the other produces a system with the same solutions.
problem_activity: Task
There were 7 children at the park. Then 4 more showed up. How many children were at the park all together?
There were 7 children at the park. Some more showed up. Then there were 11 children in all. How many more children came?
There were some children at the park. Four more children showed up. Then there were 11 children at the park. How many children were at the park to start with?


aligns: no