Solve the missing numbers in these subtraction pyramids by adding the bottom blocks or subtracting from the top.

Let's solve the subtraction pyramid puzzles step by step. In these pyramids, each number above is the sum of the two numbers directly below it, but since this is a subtraction within 100 worksheet, we need to interpret the rule correctly.

However, looking at the structure and typical design of such worksheets (especially from MathEasily.com), these are actually addition pyramids, where:

> Each number is the sum of the two numbers directly beneath it.

But the title says "Subtraction within 100", which may be misleading — in reality, these are additive pyramids, and the subtraction might refer to the types of numbers involved or the skills being practiced (e.g., subtracting to find missing values). However, based on the layout and common practice, the rule is:

> The number in a box is the sum of the two numbers below it.

So, we will use addition to fill in the blanks.

We'll go through each pyramid one by one.

---

🔹 Pyramid 1: Top = 79

```
79
39 ?
21 ? ?
9 12 ? ?
```

We know:
- 39 + ? = 79 → ? = 79 - 39 = 40
- 21 + ? = 39 → ? = 39 - 21 = 18
- So the next row: 21, 18, ?
- Now, 9 + 12 = 21 ✔
- 12 + ? = 18 → ? = 6
- Then ? + ? = 18 → so the third number in bottom row is 6
- Bottom row: 9, 12, 6, ?

Now, 18 + ? = 40 → ? = 22
So last bottom number = 22

Check: 6 + 22 = 28? Wait — no, let's rebuild carefully.

Actually, let’s label positions clearly.

#### Bottom row: A B C D
A = 9, B = 12, C = ?, D = ?

Then second row from bottom:
- First: A + B = 9 + 12 = 21 ✔
- Second: B + C = 12 + C
- Third: C + D

Third row:
- First: 21 + (B+C) = 39 → so 21 + (12 + C) = 39 → 33 + C = 39 → C = 6
- So C = 6
- Then B + C = 12 + 6 = 18
- So second block in third row is 18
- Third block: C + D = 6 + D
- Third row: 21, 18, (6+D)

Now top: 39 + ? = 79 → ? = 40

So third row must sum to 40: 21 + 18 + (6+D) = 40? No — wait!

Wait! Actually, only adjacent pairs add up to the box above.

So:
- 21 + 18 = 39 ✔
- 18 + (6+D) = 40 → 18 + 6 + D = 40 → 24 + D = 40 → D = 16

Now check bottom row: 9, 12, 6, 16

Then:
- 12 + 6 = 18 ✔
- 6 + 16 = 22 → that's the third block in second row

So second row: 21, 18, 22

Then third row: 21 + 18 = 39 ✔, 18 + 22 = 40 ✔

Top: 39 + 40 = 79 ✔

✔ So filled pyramid 1:
```
79
39 40
21 18 22
9 12 6 16
```

---

🔹 Pyramid 2: Top = 78

```
78
41 ?
19 ? ?
8 11 ? ?
```

Step-by-step:

- 41 + ? = 78 → ? = 78 - 41 = 37
- 19 + ? = 41 → ? = 41 - 19 = 22
- So second row: 19, 22, ?
- Bottom row: 8, 11, ?, ?

Now:
- 8 + 11 = 19 ✔
- 11 + ? = 22 → ? = 11 → so third number in bottom row = 11
- Then ? + ? = 22 → so fourth number = 11? Let's see.

Bottom: 8, 11, 11, ?

Then:
- 11 + 11 = 22 → second block in second row = 22 ✔
- 11 + ? = ? → third block in second row = 11 + ?

But we need: second row: 19, 22, (11 + ?)

Then third row: 19 + 22 = 41 ✔, 22 + (11 + ?) = 37 → 22 + 11 + ? = 37 → 33 + ? = 37 → ? = 4

So last bottom number = 4

Thus bottom row: 8, 11, 11, 4

Check:
- 11 + 11 = 22 ✔
- 11 + 4 = 15 → third block in second row = 15
- Then 22 + 15 = 37 ✔
- 41 + 37 = 78 ✔

✔ Filled:
```
78
41 37
19 22 15
8 11 11 4
```

---

🔹 Pyramid 3: Top = 78

```
78
33 ?
18 ? ?
10 8 ? ?
```

- 33 + ? = 78 → ? = 45
- 18 + ? = 33 → ? = 15
- So second row: 18, 15, ?
- Bottom: 10, 8, ?, ?

Now:
- 10 + 8 = 18 ✔
- 8 + ? = 15 → ? = 7 → third number = 7
- Then ? + ? = 15 → so fourth number = 8? Let's compute.

Bottom: 10, 8, 7, ?

Then:
- 8 + 7 = 15 ✔
- 7 + ? = ? → third block in second row = 7 + ?

Second row: 18, 15, (7 + ?)

Third row: 18 + 15 = 33 ✔, 15 + (7 + ?) = 45 → 15 + 7 + ? = 45 → 22 + ? = 45 → ? = 23

So last number = 23

Bottom row: 10, 8, 7, 23

Check:
- 7 + 23 = 30 → third block in second row = 30
- 15 + 30 = 45 ✔
- 33 + 45 = 78 ✔

✔ Filled:
```
78
33 45
18 15 30
10 8 7 23
```

---

🔹 Pyramid 4: Top = 98

```
98
57 ?
31 ? ?
19 12 ? ?
```

- 57 + ? = 98 → ? = 41
- 31 + ? = 57 → ? = 26
- So second row: 31, 26, ?
- Bottom: 19, 12, ?, ?

Now:
- 19 + 12 = 31 ✔
- 12 + ? = 26 → ? = 14 → third number = 14
- Then ? + ? = 26 → fourth number = 12? Let's do it properly.

Bottom: 19, 12, 14, ?

Then:
- 12 + 14 = 26 ✔
- 14 + ? = ? → third block in second row = 14 + ?

Second row: 31, 26, (14 + ?)

Third row: 31 + 26 = 57 ✔, 26 + (14 + ?) = 41 → 26 + 14 + ? = 41 → 40 + ? = 41 → ? = 1

So last number = 1

Bottom: 19, 12, 14, 1

Check:
- 14 + 1 = 15 → third block in second row = 15
- 26 + 15 = 41 ✔
- 57 + 41 = 98 ✔

✔ Filled:
```
98
57 41
31 26 15
19 12 14 1
```

---

🔹 Pyramid 5: Top = 88

```
88
47 ?
26 ? ?
13 13 ? ?
```

- 47 + ? = 88 → ? = 41
- 26 + ? = 47 → ? = 21
- So second row: 26, 21, ?
- Bottom: 13, 13, ?, ?

Now:
- 13 + 13 = 26 ✔
- 13 + ? = 21 → ? = 8 → third number = 8
- Then ? + ? = 21 → fourth number = 13? Let's see.

Bottom: 13, 13, 8, ?

Then:
- 13 + 8 = 21 ✔
- 8 + ? = ? → third block in second row = 8 + ?

Second row: 26, 21, (8 + ?)

Third row: 26 + 21 = 47 ✔, 21 + (8 + ?) = 41 → 21 + 8 + ? = 41 → 29 + ? = 41 → ? = 12

So last number = 12

Bottom: 13, 13, 8, 12

Check:
- 8 + 12 = 20 → third block in second row = 20
- 21 + 20 = 41 ✔
- 47 + 41 = 88 ✔

✔ Filled:
```
88
47 41
26 21 20
13 13 8 12
```

---

🔹 Pyramid 6: Top = 74

```
74
36 ?
20 ? ?
10 10 ? ?
```

- 36 + ? = 74 → ? = 38
- 20 + ? = 36 → ? = 16
- So second row: 20, 16, ?
- Bottom: 10, 10, ?, ?

Now:
- 10 + 10 = 20 ✔
- 10 + ? = 16 → ? = 6 → third number = 6
- Then ? + ? = 16 → fourth number = 10? Let's compute.

Bottom: 10, 10, 6, ?

Then:
- 10 + 6 = 16 ✔
- 6 + ? = ? → third block in second row = 6 + ?

Second row: 20, 16, (6 + ?)

Third row: 20 + 16 = 36 ✔, 16 + (6 + ?) = 38 → 16 + 6 + ? = 38 → 22 + ? = 38 → ? = 16

So last number = 16

Bottom: 10, 10, 6, 16

Check:
- 6 + 16 = 22 → third block in second row = 22
- 16 + 22 = 38 ✔
- 36 + 38 = 74 ✔

✔ Filled:
```
74
36 38
20 16 22
10 10 6 16
```

---

✔ Final Answer: All Pyramids Solved

Here are the completed pyramids:

#### 1.
```
79
39 40
21 18 22
9 12 6 16
```

#### 2.
```
78
41 37
19 22 15
8 11 11 4
```

#### 3.
```
78
33 45
18 15 30
10 8 7 23
```

#### 4.
```
98
57 41
31 26 15
19 12 14 1
```

#### 5.
```
88
47 41
26 21 20
13 13 8 12
```

#### 6.
```
74
36 38
20 16 22
10 10 6 16
```

---

📝 Explanation Summary:

- These are additive pyramids: each number is the sum of the two numbers directly below it.
- We used reverse addition (i.e., subtraction) to find missing values: if A + B = C, then B = C - A.
- Worked from top down or bottom up, depending on known values.
- Always checked consistency across rows.

Even though the worksheet says "Subtraction within 100", the actual operation used is addition to build the pyramid. Subtraction is used as a tool to find missing parts.

Let me know if you'd like a printable version or explanation for students!