Add and subtract numbers mentally, including a three-digit number and ones

What this means, in plain words

A digit is one of the ten symbols, 0 to 9, that all numbers are written with.

Addition puts amounts together to find a total. Subtraction takes one amount away, or finds the difference between two.

Number work here is about how our number system is built, and about knowing what a number is worth rather than just how it is spelled.