Mental Math Worksheet for Grade 1 - Exercise 20 - Your Home Teacher - Free Printable

Let's solve each problem on the Mental Math Sheet C2 step by step and explain the reasoning.

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1) ___ – 4 = 8

We need to find a number that, when 4 is subtracted from it, gives 8.

So:
x – 4 = 8
Add 4 to both sides:
x = 8 + 4 = 12

✔ Answer: 12

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2) How many mm in 9cm?

We know:
1 cm = 10 mm
So:
9 cm = 9 × 10 = 90 mm

✔ Answer: 90 mm

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3) What fraction do I need to shade to make a whole?

There are 6 rectangles in total.
2 of them are already shaded.

To make a whole (all 6 shaded), we need to shade the remaining:
6 – 2 = 4 more

So, the fraction needed to shade is 4/6, which simplifies to 2/3.

But the question asks: *"What fraction do I need to shade to make a whole?"*
That means: how much more needs to be shaded?

✔ Answer: 4/6 or 2/3

(Usually, simplest form is preferred: 2/3)

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4) Increase 479 by 200

Just add:
479 + 200 = 679

✔ Answer: 679

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5) 572¢ = $______

We know:
100 cents = $1
So divide:
572 ÷ 100 = $5.72

✔ Answer: $5.72

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6) Half a kilometer = ______ m

1 kilometer = 1000 meters
Half = 1000 ÷ 2 = 500 meters

✔ Answer: 500 m

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7) How many sides does an octagon have?

An octagon has 8 sides.

✔ Answer: 8

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8) Which is smallest?

8 inches, 8 cm, 8 m, 8 yards, 8 mm, 8 feet

Let’s convert all to millimeters for comparison:

- 8 mm = 8 mm
- 8 cm = 80 mm
- 8 inches ≈ 8 × 25.4 = 203.2 mm
- 8 feet = 8 × 12 = 96 inches → 96 × 25.4 ≈ 2438.4 mm
- 8 yards = 8 × 3 = 24 feet → 24 × 12 = 288 inches → ~7315.2 mm
- 8 m = 8000 mm

Clearly, 8 mm is the smallest.

✔ Answer: 8 mm

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9) What is the time?

Clock shows:
- Hour hand between 6 and 7 → it’s 6:something
- Minute hand pointing at 10 → 10 × 5 = 50 minutes

So the time is 6:50

✔ Answer: 6:50

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10) 800 subtract 6

800 – 6 = 794

✔ Answer: 794

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11) A CD case holds 25 CDs. How many CDs can 3 cases hold?

25 × 3 = 75 CDs

✔ Answer: 75

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12) Half of a number is 14. What is the number?

If half is 14, then full = 14 × 2 = 28

✔ Answer: 28

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13) Maisie is 5 years younger than Kyle. Kyle is 2 years older than Sam. If Sam is 8 years old, how old is Maisie?

Step-by-step:

- Sam = 8
- Kyle = Sam + 2 = 8 + 2 = 10
- Maisie = Kyle – 5 = 10 – 5 = 5

✔ Answer: 5 years old

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14) I have 375¢. I spend $2. How much money do I have left?

Convert everything to cents:

- 375¢
- $2 = 200¢

Left: 375 – 200 = 175¢

Now convert back to dollars:
175¢ = $1.75

✔ Answer: $1.75

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15) How many wheels do 6 tricycles have?

Each tricycle has 3 wheels

So: 6 × 3 = 18 wheels

✔ Answer: 18

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16) Frazer has 16 football cards which he places in piles of 4 cards. How many piles will he make?

Divide: 16 ÷ 4 = 4 piles

✔ Answer: 4

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✔ Final Answers Summary:

| # | Answer |
|---|----------------|
| 1 | 12 |
| 2 | 90 mm |
| 3 | 2/3 (or 4/6) |
| 4 | 679 |
| 5 | $5.72 |
| 6 | 500 m |
| 7 | 8 |
| 8 | 8 mm |
| 9 | 6:50 |
|10 | 794 |
|11 | 75 |
|12 | 28 |
|13 | 5 years old |
|14 | $1.75 |
|15 | 18 |
|16 | 4 |

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