Year 1: Tens and ones

Key words. A ten is a bundle of ten ones. A one is a single thing.

Method. Count the groups of ten first. Then count the ones left over.

1. Count the tens in 23. Each group of ten is one ten.
   20 is 2 tens
2. Count the ones left over. The ones are what is left after the tens.
   23 − 20 = 3 ones
3. Write the answer.
   2 tens and 3 ones

Check. Put them back together: 20 + 3 = 23. ✓

Watch out. The tens come first when you say the number. 25 is 2 tens and 5 ones, not 5 tens and 2 ones.

Key words. A ten is a bundle of ten ones. A one is a single thing.

Method. Count the groups of ten first. Then count the ones left over.

1. Count the tens in 58. Each group of ten is one ten.
   50 is 5 tens
2. Count the ones left over. The ones are what is left after the tens.
   58 − 50 = 8 ones
3. Write the answer.
   5 tens and 8 ones

Check. Put them back together: 50 + 8 = 58. ✓

Watch out. The tens come first when you say the number. 25 is 2 tens and 5 ones, not 5 tens and 2 ones.

Method. The ones are the number left over after the tens.

1. Take away the groups of ten from 69. Take away all the tens.
   69 − 60 = 9
2. Count what is left. These are the ones.
   9 ones
3. Write the answer.
   9

Check. 60 + 9 = 69. ✓

Watch out. The ones digit is the last digit of the number.

Method. Count how many groups of ten there are.

1. Count the groups of ten in 90. Count in tens: 10, 20 and so on.
   9 tens = 90
2. Check the ones left over. The ones are not tens, so they do not count here.
   0 ones left over
3. Write the answer. The number of tens is the number on the left.
   9

Check. 9 tens and 0 ones make 90. ✓

Watch out. Count the tens, not the ones. For 90, there are 9 tens and 0 ones.

Method. Start with the tens, then add the ones.

1. Write 5 tens. The tens go on the left.
   5 tens = 50
2. Add 4 ones. The ones go on the right, after the tens.
   50 + 4 = 54
3. Write the number.
   54

Check. Read it back: 54 has 5 tens and 4 ones. ✓

Watch out. The tens digit goes on the left. Write 5 tens and 4 ones as 54, not 45.

Method. Start with the tens, then add the ones.

1. Write 8 tens. The tens go on the left.
   8 tens = 80
2. Add 0 ones. The ones go on the right, after the tens.
   80 + 0 = 80
3. Write the number.
   80

Check. Read it back: 80 has 8 tens and 0 ones. ✓

Watch out. The tens digit goes on the left. Write 8 tens and 0 ones as 80, not 08.

Method. Start with the tens, then add the ones.

1. Write 1 ten. The tens go on the left.
   1 tens = 10
2. Add 9 ones. The ones go on the right, after the tens.
   10 + 9 = 19
3. Write the number.
   19

Check. Read it back: 19 has 1 tens and 9 ones. ✓

Watch out. The tens digit goes on the left. Write 1 tens and 9 ones as 19, not 91.

Method. Start with the tens, then add the ones.

1. Write 6 tens. The tens go on the left.
   6 tens = 60
2. Add 2 ones. The ones go on the right, after the tens.
   60 + 2 = 62
3. Write the number.
   62

Check. Read it back: 62 has 6 tens and 2 ones. ✓

Watch out. The tens digit goes on the left. Write 6 tens and 2 ones as 62, not 26.

Method. Start with the tens, then add the ones.

1. Write 3 tens. The tens go on the left.
   3 tens = 30
2. Add 4 ones. The ones go on the right, after the tens.
   30 + 4 = 34
3. Write the number.
   34

Check. Read it back: 34 has 3 tens and 4 ones. ✓

Watch out. The tens digit goes on the left. Write 3 tens and 4 ones as 34, not 43.

Key words. A ten is a bundle of ten ones. A one is a single thing.

Method. Count the groups of ten first. Then count the ones left over.

1. Count the tens in 62. Each group of ten is one ten.
   60 is 6 tens
2. Count the ones left over. The ones are what is left after the tens.
   62 − 60 = 2 ones
3. Write the answer.
   6 tens and 2 ones

Check. Put them back together: 60 + 2 = 62. ✓

Watch out. The tens come first when you say the number. 25 is 2 tens and 5 ones, not 5 tens and 2 ones.

Method. Most of the numbers have 7 tens. Find the one that does not.

1. Look at the tens of each number. Count the tens in each number.
   72: 7 tens   17: 1 tens   74: 7 tens   79: 7 tens
2. Find the one that is different. 17 has 1 tens. The others have 7 tens.
   17 is different
3. Write the answer.
   17

Check. Check each of the others: they all have 7 tens. ✓

Watch out. Look at the tens, not at the ones.