This, #25, in intended for the very young (UK KS1).
A selection of handmade cards are placed face-up on the table.
In every case two of the numbers add up to the same total as the other two. The difficulty lies in choosing which two.With experience there are ways to home-in one or other of the pairs, by visually scanning all four numbers. For those of a less mature mathematical mind it does require a few moments of number-bonding thought.
The main advantage of this simple tasklet is that it is self correcting. Finding two matching answers also confirms that both are correct. Secondly choosing non-matching numbers provides additional number-bond practice (although unchecked for accuracy).
The cards illustrated are part of a large selection intended for addition of every digit. In full it would include pairs adding to 18 [ 0,9 | 1,8 | 2,7 | 3,6 | 4,5 ]. There is probably no educational loss in leaving out some of these pairs.
The main task of juggling around with four digits does not have any direct comparison with everyday real-life tasks. It is the mental agility required to find the snapping pairs that is the main benefit.
Many of the cards can be used for other snaps: multiplying #37, subtraction #72.