Skip-count backward to the start

4.NBT.A.2 · take · grade 4

Archetype: Work Backwards to Recover a Start Value · step in a 9-type progression

Starting from $\blacksquare$ and skip-counting up by $10$ four times, you reach $6792$ . Find the number $\blacksquare$ .

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Starting from an unknown number ■ and skip-counting up by 10 four times lands on 6792. Find the starting number ■.

Givens

Unknowns

Constraints

#11 Work Backwards · also uses: #5 Look for a Pattern

The end result is given and we want the start, which is the classic signal to work backwards: undo each step of 10 by counting back from 6792.

#5 Look for a Pattern 2.NBT.A.2

Going up by 10 four times adds 10 four times, which is 40 in all.

4 \times 10 = 40

Four jumps of 10 stack up to 40, just like skip-counting 10, 20, 30, 40.

#11 Work Backwards 4.NBT.A.2

Since 40 was added to reach 6792, the starting number is 40 less than 6792. Counting back: 6792, 6782, 6772, 6762, 6752.

6792 - 40 = 6752

To undo adding 40, you subtract 40, landing on where you began.

Answer: 6752

Check forward: 6752 + 10 = 6762, +10 = 6772, +10 = 6782, +10 = 6792. Four jumps of 10 from 6752 reach 6792, so the start is right.

Set up the unknown directly: ■ + 40 = 6792, then subtract 40 from both sides to get ■ = 6752.

2.NBT.A.2 Count within 1000, skip-count by 5s, 10s, and 100s — Recognizing four skip-count steps of 10 as a total of 40.
4.NBT.A.2 Read and write multi-digit whole numbers and compare using symbols — Counting back by tens through four-digit numbers to reach the start.

💡 When you know where you ended up, just hop backwards the same number of tens to find where you started!