Counting & Place Value · 24 lessons

Ten digits write every whole number there has ever been. That is not a coincidence and it is not a convention we could easily have chosen differently — it is a single idea, applied over and over: a digit's worth depends on where it sits, and each column is worth ten of the one to its right.

1. 1One and One→
2. 2Counting to Ten
3. 3Ordinal Numbers
4. 4Writing Numbers to Twenty
5. 5Number Bonds to Five
6. 6More and Fewer
7. 7Counting to a Hundred
8. 8Skip Counting
9. 9Odd and Even Numbers
10. 10Tens and Ones
11. 11Number Words to a Thousand
12. 12Hundreds
13. 13Ordering Numbers
14. Place value (11)
15. 14The Thousand Cube
16. 15Numbers to Ten Million
17. 16Rounding to the Nearest Ten
18. 17Rounding to the Nearest Hundred and Thousand
19. Rounding (10)
20. 18Below Zero
21. 19Ordering Negative Numbers
22. 20Adding and Subtracting Across Zero
23. 21Significant Figures
24. 22Bounds and Error Intervals
25. 23Propagating Upper and Lower Bounds
26. 24Percentage Error