B1.1 Reading and showing numbers to 50
A two-digit number has tens and ones. In 41 there are 4 tens and 1 ones.
Example
Show 41 with blocks.
- Take 4 ten-rods. That is 40.
- Add 1 ones. 40 and 1 make 41.
- Say it: 41.
B1.2 Taking numbers apart and putting them together
You can break a number into parts and put it back together. The parts always add up to the whole.
Example
Break 41 into parts two ways.
- Tens and ones: 40 + 1 = 41.
- Another way: 36 + 5 = 41.
- Both ways make 41, because the parts add up to the whole.
B1.3 Comparing and ordering
To compare two numbers, look at the tens first. More tens means a bigger number. If the tens match, look at the ones.
Example
Which is bigger: 37 or 45?
- 37 is 37 and 45 comes later when we count.
- So 45 is bigger. We write 37 < 45.
- Compare the tens.
- Same tens? Compare the ones.
- Say which is bigger, and which is smaller.
B1.4 Estimating, then counting
An estimate is a careful guess. Look at a group, guess about how many, then count to check.
Example
About how many marbles are there? Estimate, then count.
- Guess: it looks like about 21.
- Count by ones to check: there are 24.
- Close! A good estimate is near the real count.
B1.5 Counting by 1s, 2s, 5s and 10s
Skip counting means jumping by the same amount each time. By 2s: 2, 4, 6. By 5s: 5, 10, 15. By 10s: 10, 20, 30.
Example
Count by 5s from 0.
- 5, 10, 15, 20, 25.
- Every jump adds 5.
B1.6 Fair shares with some left over
A fair share means everyone gets the same. Sometimes there is 1 or 2 left over — that is okay.
Example
Share 7 cookies fairly between 2 friends.
- Deal them out: one for you, one for me, again and again.
- Each friend gets 3 cookies.
- 1 cookie is left over. 3 + 3 + 1 = 7.
B1.7 One half and two fourths
Example
Is one half the same as two fourths?
- Cut a pizza into 2 equal parts. Take 1 part: one half.
- Cut another into 4 equal parts. Take 2 parts: two fourths.
- Put them side by side. Same amount! One half = two fourths.
B1.8 More sharers, smaller pieces
Example
One bar is shared by 2 people. Another is shared by 4. Who gets a bigger piece?
- Shared by 2: each piece is one half.
- Shared by 4: each piece is one fourth.
- One half is bigger than one fourth. More sharers means smaller pieces.
Summary
- Tens and ones build numbers to 50.
- Compare tens first.
- Estimate, then count.
- Fair shares are equal; more sharers, smaller pieces.