Mental math worksheet for adding and subtracting numbers, including calculations and part-whole models.

Let's solve the worksheet step by step and explain each part.

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Section A: Complete the calculations

We need to add or subtract numbers mentally.

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1) 500 + 30 + 2 = ?
Add step by step:
500 + 30 = 530
530 + 2 = 532

✔ Answer: 532

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2) 100 + 90 + 7 = ?
100 + 90 = 190
190 + 7 = 197

✔ Answer: 197

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3) 5 + 500 + 60 = ?
Group in order:
500 + 60 = 560
560 + 5 = 565

✔ Answer: 565

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4) two hundred + thirty + one = ?
Convert words to numbers:
200 + 30 + 1 = 231

✔ Answer: 231

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5) 80 + 200 + 4 = ?
80 + 200 = 280
280 + 4 = 284

✔ Answer: 284

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6) 4 + 20 + [ ] = 124
First, add known values:
4 + 20 = 24
Now find missing number:
124 − 24 = 100

✔ Answer: 100

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7) 70 + [ ] + 4 = 674
Add knowns:
70 + 4 = 74
Now subtract from total:
674 − 74 = 600

✔ Answer: 600

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Section B: Complete the part-whole models

These are visual models where the top circle is the whole, and the bottom circles are parts.
So:
> Whole = Part + Part

We use addition and subtraction to fill in missing numbers.

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1)
Whole = ?
Parts: 100 and 4
→ 100 + 4 = 104

✔ Top circle: 104

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2)
Whole = ?
Parts: 700, 20, 2
→ 700 + 20 = 720; 720 + 2 = 722

✔ Top circle: 722

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3)
Whole: 370
One part: 300
Other part = 370 − 300 = 70

✔ Bottom right circle: 70

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4)
Whole: 699
One part: 9
We need to split the rest into two parts. But there are three parts below, so we assume the top (whole) is made of three parts:
Let’s suppose it's a three-part model:
699 = [ ] + [ ] + 9

But no other numbers given. So we can only find the sum of the two missing parts:
699 − 9 = 690 → These two circles must add to 690.

But since no further info, perhaps they expect us to break 690 into two parts — but without more constraints, any pair that adds to 690 works? That seems unlikely.

Wait — maybe it's a two-part model with one part already split?

Looking at the diagram:

- Top: 699
- Below: three circles: left blank, middle blank, right: 9

This suggests that the whole (699) is made of three parts: left, middle, and 9.

So:
Left + Middle + 9 = 699
→ Left + Middle = 690

But still two unknowns. Not enough info unless we assume standard place value.

Wait — maybe it's a hundreds, tens, units breakdown?

Let’s check:
699 = 600 + 90 + 9

So:
- Left: 600
- Middle: 90
- Right: 9

✔ So:
- Left circle: 600
- Middle circle: 90

That makes sense.

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5)
Whole: 107
One part: 100
Other part = 107 − 100 = 7

✔ Right circle: 7

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6)
Whole: 266
One part: 60
We need to split the rest into two parts.

266 − 60 = 206 → This is the sum of the other two parts.

But again, two blanks. Let's think about place value.

266 = 200 + 60 + 6

So:
- Left: 200
- Middle: 60
- Right: 6

✔ So:
- Left circle: 200
- Right circle: 6

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✔ Final Answers:

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#### Section A:
1) 532
2) 197
3) 565
4) 231
5) 284
6) 100
7) 600

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#### Section B:
1) 104
2) 722
3) 70
4) 600, 90, 9 → left: 600, middle: 90, right: 9
5) 7
6) 200, 60, 6 → left: 200, middle: 60, right: 6

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📌 Explanation Summary:

- In Section A, we used mental addition and subtraction, breaking numbers into hundreds, tens, and units.
- In Section B, the "part-whole" models represent how a number is composed of its parts. We used:
- Addition to find the whole (when parts are known)
- Subtraction to find a missing part (when whole and some parts are known)
- Place value knowledge (hundreds, tens, ones) to split numbers logically.

These strategies help build mental math fluency and number sense.

Let me know if you'd like this as a printable answer key!