Problem
Skip-count backward to the start
From ■, skip-counting up by 10 four times reaches 6792. What is the start ■?
Base-ten numbers
Your answer
Watch out 6792 is the ending number. Don't count forward again — you must go backward to reach the start.
How to solve
1STEP 1
Find the total amount added
Four jumps of 10 add 10 four times — a total of 40 piles up.
4 × 10 = 40
Four jumps of 10 are four equal groups of 10, so adding 10 four times makes 40 — exactly what the skip-counting added on.
Look For A Pattern2.NBT.A.22STEP 2
Count back from the ending number
6792 is the start plus 40 — take that 40 back off to land on the start, 6752.
6792 − 40 = 6752
Removing exactly the amount that was added lands you back at the start, since subtracting reverses adding — so 6792 minus 40 hits the starting number.
Work Backwards4.NBT.A.2Four Digit NumbersYou find the starting number by subtracting 40 from 6792, because 40 is exactly what the skip-counting added on.
Why?
The four counts up by 10 piled a total of 40 onto the start, so 6792 is just the start with 40 added; taking that same 40 back off returns to the start.
Why?
Removing exactly the amount that was added lands you back where you began, since taking away reverses adding on.
🧱Inverse operationsSubtraction undoes addition and division undoes multiplication — they reverse each other.
Why?
The amount to take back off is 40 because four jumps of 10 add up to 40.
Why?
Four jumps of 10 are four equal groups of 10, and adding 10 four times makes 40.
🧱Multiplication as equal groupsa times b means a equal groups of b — it is just repeated adding of the same amount.
Answer
6752
6792 − 40 = 6752
Check — from 6752 count forward: 6762, 6772, 6782, 6792. Four jumps of 10 reach 6792, so the start is right.
Takeaway
When you know where it ended, work backward. Subtract the 40 the jumps added to recover the start, 6752.
- Find what was added (4 × 10 = 40)
- Subtract it back (6792 − 40)
- The start is 6752
Where next?
Level upsuggested
Another one like thissuggested
Same look, different logicsuggested
Step back and solidifysuggested