Grade 1 Subtraction Within 20, Solved at Asteroid Speed

An asteroid belt sits between the rocket and the station, and each rock carries a number. Fifteen take away six — find the 9 and blast it. What makes this harder than a worksheet is that the wrong answers are moving too, so a first grader can't scan a row and eliminate. They have to commit. Subtraction within 20 is where the link between adding and subtracting starts paying off, and children who think "six plus what makes fifteen" get through the belt noticeably faster.

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What this station asks for

☄️ Through the Asteroid BeltAsteroids block the docking bay! Work out each subtraction, then blast the asteroid showing that number. Sharp eyes, Agent! You solve each problem and tap the drifting space rock that carries the answer. Five tasks, then a boot print goes into the Case File.

Five questions it might ask

Drawn from the same pool the activity uses, so these are the real thing rather than an illustration. The numbers change on every attempt — there is no fixed set to memorize.

Question	Answer
12 − 7 = ?	5
10 − 4 = ?	6
8 − 6 = ?	2
13 − 4 = ?	9
9 − 7 = ?	2

👀 What to watch for

If a child freezes on problems that cross ten — 15 − 6, 14 − 8 — that's normal and it's the actual content of first grade. The ones that don't cross ten are usually already fluent. Steering them toward the matching addition fact is the most reliable unlock.

The Common Core standard behind it

Official wording, quoted in full — not our summary of it:

1.OA.C.6	Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten; decomposing a number leading to a ten; using the relationship between addition and subtraction; and creating equivalent but easier or known sums.

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Other Grade 1 skills in this case

Addition within 201.OA.C.6 Number bonds to 201.OA.C.6 Adding tens within 1001.NBT.C.4

All grades

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