1st Grade Complete the Subtraction Worksheet: Missing Numbers to 20

Show a six-year-old 18 - __ =17 and many will say 1 right away, while __ -2 = 17 can stop them for a long moment. Both are the same kind of puzzle, seen from two sides. This 1st grade complete the subtraction worksheet up to 20 gives your child plenty of both. Eight colored boxes each hold four sentences with one dotted blank, and inside each box, all four sentences share the same answer, such as 17, 9 or 15. Sometimes the blank is the first number, and sometimes it is the number being taken away. A group of cartoon animals peeks in from the top corner. A second page gives the answer key.

Why the blank moves from place to place

Most early subtraction asks for the answer at the end. Putting the missing number at the start or in the middle forces a different question: what fits here? That shift helps children see subtraction as a relationship between three numbers, not just a recipe.

The page arranges this cleverly. Every box keeps the same answer, so your child can compare the four sentences. For example, in the box for 16, two sentences hide the start number and two hide the part taken away.

Also, a blank before the minus sign often calls for addition. To solve __ -4 = 16, a child can think addition: 16 and 4 make 20. So the page links the two operations without saying so. Clever, and quiet.

At the table: 17 - __ =17

Start with the green box at the top left. Ask your child to read 18 - __ =17 aloud. "How many did we take from 18?"

The last sentence in that box, 17 - __ =17, is the one that surprises. Children often write 1, because the other answers nearby are small. Instead of correcting, ask, "If 17 stays 17, how many did we take away?" Let your child hold up a closed fist and decide.

The blanks at the start are the other trap, as in __ -10 = 9 in the pink box. A child may subtract 10 - 9 and write 1. Point to the blank and ask, "Is this the number we start with?" Then let your child count up from 9.

Counting games with a missing piece

Missing numbers show up in daily life more than we notice. While you put away the shopping, count the cans, hide a few behind your back, and ask how many are hiding. At the table, lay out sixteen crackers, cover some with a napkin, and let your child find how many hide.

Also, Hide and Seek is a ready partner. The seeker counts to 20, so stop at 14 and ask, "How many numbers are still to go?" That is subtraction within 20 in disguise.

Finally, check the page with the answer key together and name the work: "You checked each box by thinking about the answer."