B1.1 Hundreds, tens and ones
Numbers past 100 have hundreds, tens and ones. In 145 there is 1 hundred, 4 tens and 5 ones: .
Example
Take 145 apart, then put it back together.
- Apart: 100 + 40 + 5.
- Another way: 140 + 5.
- Together again: 145. We see numbers like this on doors, buses and page numbers.
B1.2 Comparing and ordering to 200
Compare the hundreds first, then the tens, then the ones. A number with more hundreds is bigger, no matter its ones.
Example
Order 148, 138, 183 from least to greatest.
- Look at hundreds, then tens.
- 138 is the smallest. 148 is next. 183 is the greatest.
- Least to greatest: 138, 148, 183.
B1.3 Estimating bigger collections
To estimate a big collection, find a group of 10 with your eyes, then think how many tens there might be. Then count to check.
Example
About how many blocks? Estimate, then count by 10s.
- Circle a group of 10. Picture that group again and again.
- Estimate: about 4 tens, so about 40.
- Count by 10s to check: there are 48. A good estimate is close.
B1.4 Counting by 20s, 25s and 50s
Example
Count by 25s to 200.
- 25, 50, 75, 100 … all the way to 200.
- Each jump adds 25.
- Counting by 25s is like counting quarters; by 20s is like counting twenty-dollar bills.
B1.5 Even and odd
An even number can be split into two equal groups with none left over. An odd number always has one left over. Look at the ones digit: 0, 2, 4, 6, 8 are even; 1, 3, 5, 7, 9 are odd.
Example
Is 14 even or odd? Is 27?
- 14 makes 7 pairs with none left over: even.
- 27 makes 13 pairs with 1 left over: odd.
- Quick check: the ones digit of 14 is 4 (even); of 27 is 7 (odd).
B1.6 Fair shares: wholes, halves and leftovers
When we share, each person can get a whole number, or a whole and a part (like 3 and a half), or just a part. Draw it to see.
Example
Share 7 granola bars between 2 friends.
- Give each friend 3 bars. 1 bar is left.
- Cut the last bar in half. Each friend gets one more half.
- Each friend gets 3 and a half bars.
Example
Share 10 bars among 4 friends. Who gets more — these friends, or the 2 friends above?
- 10 among 4: each gets 2, and 2 bars are left. Cut each in half: 4 halves, one each.
- Each of the 4 gets 2 and a half.
- 3 and a half is more than 2 and a half: fewer sharers, bigger share.
B1.7 One third and two sixths
Example
Is one third the same as two sixths?
- Cut a pie in 3 equal parts. Take 1: one third.
- Cut the same size pie in 6 equal parts. Take 2: two sixths.
- Match them up: the same amount. .
Summary
- Hundreds, tens, ones to 200.
- Compare hundreds first.
- Even splits in two; odd leaves one.
- Shares can be wholes, halves, or parts; one third = two sixths.