Start from zero — the basic math you need before everything else
Adding combines amounts into one total. Subtracting takes some away, or finds the difference between two amounts. They are opposites. Subtraction undoes addition.
For numbers with more than one digit, line them up by place value and work the columns from right to left. If a column adds to more than 9, write the ones digit and carry the extra ten into the next column. When subtracting, if the top digit is too small, borrow ten from the column to its left.
Carrying and borrowing are just bundling. Picture eggs: ten loose eggs snap into one carton of ten. When a column tops 9, you bundle ten of them into a single unit and slide it one column left — that's a carry. Borrowing is the reverse: you crack open one carton back into ten loose eggs so the column has enough to take from.
▶ Adding & Subtracting