Mental Maths Questions

We all know mental maths is an essential skill while performing mathematical calculations. Mental maths questions with solutions and tricks are provided here for students to improve their mental calculation skill. Train your brain with these mental maths questions and perform any arithmetic calculations within seconds.

Also refer:

• Mental Maths for Class 2
• Mental Maths for Class 5
• Maths Quiz Questions

Let us have a look at some shortcuts to do addition and subtraction mentally.

• Addition without carrying: Suppose we have to add two numbers 35 + 89

Step I: 30 + 80 = 110

Step II: 110 + 5 = 115

Step III: 100 + (15 + 9) = 124

• Addition by grouping: Suppose we have to add numbers 90 + 19 + 51

Step I: 19 = 10 + 9

Step II: 90 + 10 = 100

Step III: 51 + 9 = 60

Step IV: 100 + 60 = 160

• Left-to-right Addition: Generally, we are taught to add numbers from right to left. But while adding mentally, it sometimes becomes hard to recall the numbers backwards after calculating them right to left. Use this method to calculate quickly.

For example, 59 + 23

Step I: 59 + 20 = 79

Step II: 79 + 3 = 82

• Subtracting by Rounding: While subtracting numbers, if one number can be rounded to the nearest tens, hundreds or thousands makes our calculation easier.

For example: 346 – 96

Step I: Add 4 to 96, 96 + 4 = 100

Step II: 346 – 100 = 246

Step III: 246 + 4 = 250

• Subtract by Adding: This technique work when we have to subtract a single-digit number from a teen number.

Example: 11 – 7

Step I: 10 – 7 = 3

Step II: Add the ones-digit of 11 to 3, 1 + 3 = 4

• Left-to-right subtraction: Just the same process as left-to-right addition.

For example: 385 – 178

Step I: 385 – 100 = 285

Step II: 285 – 70 = 215

Step III: 215 – 8 = 207 (here we can use the trick to subtract a single-digit number from a teen number)

• Subtraction without Borrowing: Suppose we have to subtract 2176 from 3456:

3456 – 2176

In the tens place, we see that there is 5 – 7 which is not possible hence we take 45 – 17 which is possible, and 45 – 17 (we can find this by subtraction by rounding).

Thus, 45 – 17 = 28

∴ 3456 – 2176 = 1280.

Mental Maths Questions with Solution

Let us practice some mental maths questions to train our brain.

Question 1: Calculate mentally:

(i) 120 + 80 + 756 + 40

(ii) 74 + 23

(iii) 57 + 89

(iv) 340 + 30 + 40

(v) 208 + 92

Solution:

(i) 120 + 80 + 756 + 40 = 996

We shall use the addition by grouping

120 + 80 = 200

50 + 40 + 6 = 96

700 + 200 + 96 = 996

(ii) 74 + 23 = 97

We shall use left-to-right addition

74 + 20 = 94

94 + 3 = 97

(iii) 57 + 89 = 146

We can use addition without carrying but it is easier to use addition with grouping

(56 + 1) + 89 = 56 + 90 = 146

(iv) 340 + 30 + 40

We can use addition by grouping

40 × 2 + 30

= 80 + 30 = 110

110 + 300 = 410

Question 2: Calculate mentally:

(i) 12 – 8

(ii) 17 – 9

(iii) 294 – 189

(iv) 34 – 27

(v) 2378 – 1876

Solution:

(i) 12 – 8 = 4

We use the trick to subtract a single-digit number from a teen number.

10 – 8 = 2

2 + 2 = 4

(ii) 17 – 9 = 8

We use the trick to subtract a single-digit number from a teen number.

10 – 9 = 1

7 + 1 = 4

(iii) 294 – 189 = 105

We shall use the technique of subtraction without borrowing

94 – 89 = 5 (Use subtraction by rounding)

∴ 234 – 189 = 105

(iv) 34 – 27 = 7

Use subtraction by rounding

34 – 30 = 4

∵ 27 + 3 = 30

∴ 4 + 3 = 7

Question 3: Calculate mentally:

(i) 248 – 25 + 87

(ii) 305 + 45 + 23

(iii) 820 + 23 – 20

Solution:

(i) 248 – 25 + 87 = 310

Step I: 248 + 87 = 245 + 90

= 200 + (90 + 45)

= 200 + 135 = 335

Step II: 335 – 25 = 310

(ii) 305 + 45 + 23 = 373

300 + (45 + 5) = 350

350 + 20 = 370

370 + 3 = 373

(iii) 820 + 23 – 20 = 823

23 – 20 = 3

820 + 3 = 823

Also Read:

• Vedic Mathematics Tricks
• Maths Tricks
• Multiplication Tricks
• Divisibility Rules

Question 4: Calculate mentally:

(i) 14 × 11

(ii) 98 × 11

(iii) 47 × 11

(iv) 456 × 11

Solution:

(i) 14 × 11 = 154

Caluclate like this, 14 × 11 = 1(1+4)4.

(ii) 98 × 11 = 1078

Since, 9(9+8)8 = 9(17)8 = 1078

1 of 17 is carried over to 9, 9 + 1 = 10.

(iii) 47 × 11 = 517

Since, 4(4+7)7 = 4(11)7 = 517

1 of 11 is carried over to 4, 4 + 1 = 5.

(iv) 456 × 11 = 5016

Just add 4560 + 456 = 5016.

Question 5: Calculate mentally:

(i) 26 × 25

(ii) 35 × 17

(iii) 46 × 15

(iii) 154 × 25

Solution:

(i) 26 × 25 = 650

Half 26 and double 25, 13 × 50

Now, 13/2 = 6.5 and 6.5 × 100 = 650.

(ii) 35 × 17 = 595

Half 17 and double 35, so that we get 8.5 × 70

Simply calculate 85 × 7 = (80 + 5) × 7 = 560 + 35 = 595.

(iii) 46 × 15 = 690

Half 46 and double 15, so that we get 23 × 30 = 690.

(iv) 154 × 25 = 3850

Half 154 and double 50, so that we get 77 × 50

Then, 77/2 × 100 = 38.5 × 100 = 3850.

Question 6: Calculate mentally:

(i) 387 ÷ 2

(ii) 8761 ÷ 2

(iii) 47 ÷ 2

(iv) 91 ÷ 2

Solution:

(i) 387 ÷ 2 = 193.5

386 ÷ 2 = 193

∴ 387 ÷ 2 = 193.5

(ii) 8761 ÷ 2 = 4380.5

(iii) 47 ÷ 2 = 23.5

(iv) 91 ÷ 2 = 45.5

Question 7: Calculate:

(i) 234 ÷ 25

(ii) 827 ÷ 5

(iii) 1356 ÷ 125

(iv) 187 ÷ 50

Solution:

(i) 234 ÷ 25 = 9.36

Step I: 234 × 4 = 936

Step II: 936/100 = 9.36

(ii) 827 ÷ 5 = 165.4

Step I: 827 × 2 = 1654

Step II: 1654/10 = 165.4

(iii) 1356 ÷ 125 = 10.848

Step I: 1356 × 8 = 10848

Step II: 10848/1000 = 10.848

(iv) 187 ÷ 50 = 3.74

Step I: 187 × 2 = 374

Step II: 374/100 = 3.74

Question 8: Calculate the following:

(i) 282 ÷ 75

(ii) 45 ÷ 75

(iii) 351 ÷ 75

Solution:

(i) 281 ÷ 75 = 3.76

Step I: 282 ÷ 3 = 94

Step II: 94 × 4 = 376

Step III: 376 ÷ 100 = 3.76

(ii) 45 ÷ 75

Step I: 45 ÷ 3 = 15

Step II: 15 × 4 = 60

Step III: 60 ÷ 100 = 0.6

(iii) 351 ÷ 75

Step I: 351 ÷ 3 = 117

Step II: 117 × 4 = 468

Step III: 468 ÷ 100 = 4.68

Question 9: Convert the following into percentages:

(i) 3.4/17 (ii) 18/50 (iii) 29/45

Solution:

(i) 3.4/17 = 20%

Step I: 3.4 × 100 = 340

Step II: 340/17 = 20%

(ii) 18/50 = 360%

Step I: 18 × 100 = 1800

Step II: 1800/50 = 36%

(iii) 29/45 = 64.44% (approx)

Step I: 29 × 100 = 2900

Step II: 2900/45 = 64.44

Question 10: Evaluate the following:

(i) 7% of 250 (ii) 16% of 45

Solution:

(i) 7% of 250 = 17.5

Step I: 7/10 = 0.7 and 250/10 = 25.0

Step II: 0.7 × 25 = 17.5

= 17.5

(ii) 16% of 45 = 7.2

Step I: 16/10 = 1.6 and 45/10 = 4.5

Step II: 1.6 × 4.5 = 7.2

Practice Questions on Mental Maths

1. Calculate mentally:

(i) 2896 + 386

(ii) 345 + 90

(iii) 347 – 94

(iv) 12 – 34 + 4

(v) 267 – 56 – 32

(vi) 11 × 234

(vii) 25 × 116

(viii) 567 ÷ 2

(ix) 1947 ÷ 2

(x) 239 ÷ 25

2. Convert the following into percentages:

(i) 38/7 (ii) 65/8 (iii) 45/3

3. Evaluate the following:

(i) 12% of 225 (ii) 11% of 200

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