Study guide: Think in Tens and Ones
Build, compare, and change two-digit numbers using groups of ten.
Ideas to explain in your own words
- Explain a two-digit number as groups of ten and leftover ones.
- Use place value to decide which two-digit number is greater.
- Find ten more by changing the tens and keeping the ones.
- Find a difference by removing groups of ten.
Watch your reasoning
- One ten is 10 and six ones are 6. Together they make 16. Six tens and one one would make 61.
- Both numbers have six tens. Three ones are fewer than eight ones, so 63 < 68.
- 46 has four tens and six ones. Adding one ten gives five tens and six ones: 46 + 10 = 56.
- Eight tens minus three tens leaves five tens: 80 − 30 = 50. The answer is fifty, not five single dots.
A worked review example
Build a Number with Tens and Ones: 14 = 1 ten + 4 ones = 10 + 4. The digit 1 stands for ten, not for one single dot. Compare Tens Before Ones: 42 = 40 + 2 and 37 = 30 + 7. Forty-two is greater because it has four tens. For 54 and 58, the tens tie; 4 < 8, so 54 < 58. Add One Whole Ten: 24 + 10 = (20 + 4) + 10 = 30 + 4 = 34. Three ten-boxes hold thirty dots and the four loose dots make thirty-four. Take Away Whole Tens: 60 − 20 = 40 because six tens minus two tens leaves four tens. The check is 40 + 20 = 60.
Make a practice plan
- Try the supplied lesson problems without looking at the answers.
- Compare your method with the worked examples and explain any correction.
- Use the new review cases, then complete the transfer task on paper or in your own document.