Problem
Find the constant skip-count step
Four evenly spaced ticks 3829·3929·4029·4129 were made by skip-counting by the same step. How big is one step (●)?
Base-ten numbers
Your answer
Watch out One step is the gap between neighbors, not the span from first to last
How to solve
1STEP 1
Subtract two neighbors
The gap between two neighbors is one step. 3929 minus 3829 is 100.
3929 − 3829 = 100
Skip-counting reaches each next tick by adding the same step, so 3929 is 3829 with one step added on. Subtraction undoes that addition, so 3929 minus 3829 leaves just the step.
Look For A PatternFour Digit Numbers4.NBT.A.2One skip-count step equals the difference between two neighboring labels, 3929 minus 3829.
Why?
Skip-counting builds the line by adding the same step to reach each next tick, so 3929 is 3829 with exactly one step added on.
Why?
Skip-counting by a fixed size is just adding that same amount over and over, so every hop from one tick to the next adds one identical step.
🧱Multiplication as equal groupsa times b means a equal groups of b — it is just repeated adding of the same amount.
Why?
Because 3929 is 3829 plus one step, taking 3829 away from 3929 gives that step back.
Why?
Subtraction is the reverse of addition, so it undoes the added step and leaves the step by itself.
🧱Inverse operationsSubtraction undoes addition and division undoes multiplication — they reverse each other.
2STEP 2
Confirm the step repeats
Every other gap is 100 too — so the skip step is 100.
4029 − 3929 = 100 · 4129 − 4029 = 100
If the jumps are evenly spaced, every neighboring pair must differ by the same amount. All three gaps are 100, so these numbers are exactly the pattern of counting by 100.
Draw A DiagramLook For A Pattern2.NBT.A.2Answer
100
3929 − 3829 = 100
Check — counting on by 100 from 3829 gives 3929, 4029, 4129, exactly the labels shown. Even the first-to-last span 300 split over three jumps is 300 ÷ 3 = 100.
Takeaway
For evenly skip-counted numbers, subtract two neighbors to find one step — it's the gap of one tick, not the whole span.
- Subtract two neighbors (3929 − 3829)
- Check every gap matches
- One step = 100
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