Cardinality to 20

Cardinality to 20 practice with visual examples, common slips, and next-step routes.

Surface

This skill appears in Keyed finite-set matching and unmatched-target count.

Task formats

Keyed finite-set matching and unmatched-target count

Keyed finite-set matching and unmatched-target count asks the player to complete an injective key-preserving match, then enter the derived count of unmatched targets.

ActionComplete an injective key-preserving match, then enter the derived count of unmatched targets.

CheckComplete the keyed finite-set matching and unmatched-target count action.

UseSupport / Core / Transfer

ShowsCheck only

PresentationCompact / Standard / Extended

Practice focus

Math facts / times tables / Number sense and place value

Selection

Fresh independent work can move toward Core, Transfer, or Challenge routes; help use or confusion keeps support visible.

Help

Hints keep attention on the visible structure; reveals show the path without counting as independent evidence.

Presentation

Presentation can reduce reading and interaction load without changing the selected skill. Practice focus can bias compatible work without breaking prerequisites or story fit.

Story fit

Episodes whose mathematical action is build complete key-preserving finite matches and derive unmatched-set cardinality from the validated construction.