1
Breaking numbers into tens and ones
Discover Mathematics P2: Term 1, Lessons 31–40
GoalBreak a two-digit number into tens and ones in more than one way.
New words
decompose · to break a number into smaller partstens · groups of tenones · single things
Explanation
We can break a number into tens and ones. 42 has 4 tens and 2 ones, so 42 = 40 + 2. There is another way. Break one ten into 10 ones. Now 42 is 3 tens and 12 ones, so 42 = 30 + 12. Both ways make the same number. Drawing sticks for tens and dots for ones helps us see the parts.
Worked examples
42 = 4 tens and 2 ones = 40 + 2.
37 can be 3 tens and 7 ones (30 + 7) or 2 tens and 17 ones (20 + 17).
56 = 50 + 6, and also 56 = 40 + 16.
Class activity
Bundle beans or sticks. Make 37 with 3 bundles of ten and 7 single ones. Now open one bundle and show 2 bundles and 17 ones. Count to check that it is still 37.
Practice
1
Break 85 into tens and ones.
80 + 5 (8 tens and 5 ones)
2
How many tens and ones are in 62?
6 tens and 2 ones
3
Which number is 3 tens and 5 ones?
35
4
Break 22 in another way, with 1 ten.
10 + 12
5
56 = 4 tens and ? ones.
16