Find the Missing Number — Ocean Life — Grade 1

The unknown here is the amount removed, not the answer. A group of fish, crabs and an octopus is pictured, the number left is written, and the child finds how many were taken away to get there. That is change-unknown subtraction — a step beyond plain take-away, because the child reasons about the missing middle. Kept within twenty, it leans on counting up and on knowing which take-away makes the result, and the pictured sea creatures keep that reasoning anchored to something a child can count.

Change-unknown subtraction builds the idea that start, change, and result are linked — that knowing two of them gives the third. A child who finds the amount removed is reasoning about that relationship, not just performing a take-away, which is exactly the Grade 1 growth this targets. Pictured sea creatures and within-twenty numbers keep it concrete.

Children who like ocean life take to the puzzle of working backward, and it suits a child ready for a little more than plain take-away. When this feels easy, try find the missing number with pets, or find the missing number with things that fly. You can also browse every subtraction worksheet or the whole sea creatures collection for grade 1 — each sheet prints cleanly in black and white or plays online for free.