Drag and drop the number from the right to the number on the left so they both add up to 30.
In other words: Click and hold the button down while moving the number. Release the button when over the other number.
The resources listed below are aligned to the same standard, (2NBT05) re: Common Core Standards For Mathematics as the Addition and subtraction game shown above.
Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.