Decomposition math worksheet for breaking numbers into tens and units using a tree diagram.

Let’s solve each number by breaking it into tens and units.

Remember:
- The “tens” part is how many groups of 10 are in the number.
- The “units” part is what’s left over (the ones digit).

We’ll go one by one:

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19 → 1 ten and 9 units → 10 and 9

15 → 1 ten and 5 units → 10 and 5

14 → 1 ten and 4 units → 10 and 4

11 → 1 ten and 1 unit → 10 and 1

10 → 1 ten and 0 units → 10 and 0

16 → 1 ten and 6 units → 10 and 6

17 → 1 ten and 7 units → 10 and 7

12 (again) → 1 ten and 2 units → 10 and 2

13 → 1 ten and 3 units → 10 and 3

18 → 1 ten and 8 units → 10 and 8

20 → 2 tens and 0 units → 20 and 0

Wait — let’s double-check 20.
20 = 10 + 10, so that’s two tens. But since we’re breaking into “tens and units”, and 20 has no leftover units, it’s 20 (as the tens part) and 0 (units). That’s correct.

Actually — hold on! In decomposition like this, for numbers 10–19, we usually break as 10 + [unit]. For 20, it’s 20 + 0? Or should we think of it as 10 + 10? But looking at the first example: 12 was broken into 10 and 2 — so they’re using “tens” to mean the multiple of 10 that fits, and “units” as the remainder.

So for 20:
Tens = 20 (because 20 is 2×10), Units = 0 → So yes, 20 and 0

But wait — in some curricula, they might expect “10 and 10” for 20? Let’s check the pattern.

Looking back: All other numbers from 10–19 are split as 10 + unit. Only 20 is different.

In the diagram, the top circle is the full number, and the two bottom circles are the parts. For 12, it’s 10 and 2. So for consistency, 20 should be broken as 20 and 0? Or maybe 10 and 10?

Actually — let’s think: If you have 20, how many tens? Two tens. But the worksheet says “break down into tens and units”. In place value, 20 is 2 tens and 0 units. But here, they’re not asking for digits — they’re asking to split the number additively into a multiple of 10 and the rest.

For 12: 10 + 2
For 19: 10 + 9
For 20: It could be 20 + 0, or 10 + 10. Which one fits the pattern?

Looking at the structure: Each top number connects to two bottom numbers that add up to it. And for 12, they used 10 and 2 — which is standard decomposition for teens.

For 20, if we follow the same logic, since 20 is not a teen, but still a multiple of 10, the most consistent way is to use 20 and 0 — because 10 + 10 would be splitting into two equal tens, but the worksheet seems to want “the big chunk of ten(s)” and “what’s left”.

But actually — let’s look again at the instruction: “Break these numbers down into tens and units”

In math education, especially for young students, “tens and units” often refers to place value decomposition.

So:
- 12 = 1 ten and 2 units → written as 10 and 2
- 20 = 2 tens and 0 units → but how do we write that? As 20 and 0? Or as 10 and 10?

I think for consistency with the format shown (where 12 is split into 10 and 2), they probably expect for 20 to be split into 20 and 0 — because 20 is the “tens” part (meaning the total value of the tens place) and 0 is the units.

Alternatively, maybe they want the largest multiple of 10 less than or equal to the number, and the remainder.

For 20: largest multiple of 10 ≤ 20 is 20, remainder 0 → so 20 and 0.

Yes, that makes sense.

Let me verify all:

Row 1:
- 12 → 10, 2 ✔ (given)
- 19 → 10, 9
- 15 → 10, 5

Row 2:
- 14 → 10, 4
- 11 → 10, 1
- 10 → 10, 0

Row 3:
- 16 → 10, 6
- 17 → 10, 7
- 12 → 10, 2

Row 4:
- 13 → 10, 3
- 18 → 10, 8
- 20 → 20, 0

All additions check out:
10+9=19, 10+5=15, etc., and 20+0=20.

Perfect.

Final Answer:
Here are the decompositions for each number:

- 19 → 10 and 9
- 15 → 10 and 5
- 14 → 10 and 4
- 11 → 10 and 1
- 10 → 10 and 0
- 16 → 10 and 6
- 17 → 10 and 7
- 12 → 10 and 2
- 13 → 10 and 3
- 18 → 10 and 8
- 20 → 20 and 0