**Mental Maths**

#
**Mental Math Multiplication Strategies**

- Mental maths is defined as the ability to solve the arithmetic calculation mentally using the tricks.
- It takes less time to solve the problem.
- It increases the problem-solving ability in children.
- Regular practice of mental sums improves the child sense in numbers.

## Mental Math Multiplication Tricks

Multiplication of a whole number with the multiples of 10:

- Multiply the non-zero part of both the factors.
- Count the number of zeros in each of the factor.
- Add the same number of zeros in the product.

Examples 1:

Multiply 2100 by 400.

**Solution: **

Step 1: Multiply 21 by 4

21 × 4 = 84

Step 2: Total number of zeros in each of the factor = 4.

Step 3: Add 4 zeros in the product
84.

840000

Therefore, 21 × 4 = 8,40,000.

Examples 2:

Multiply 100 by 1000.

**Solution: **

Step 1: Multiply 1 by 1

1 × 1 = 1

Step 2: Total number of zeros in each of the factor = 5.

Step 3: Add 5 zeros in the product
1

100000

Therefore, 100 × 1000 = 1,00,000.

Multiplication of two digits number by a two digits number:

Step 1: Multiply the unit digit of both the numbers.

Step 2: Multiply the unit digit of multiplier by the ten digit of multiplicand and the ten digits of multiplier by the unit digit of multiplicand. Add them together.

Step 3: Multiply the ten digits of both the number.

Examples :

Multiply 57 by 62.

**Solution: **

Multiplication of two digits number by a two digits number when the ten digits are same and the sum of unit digit is 10:

Step 1: Multiply both the unit digits.

Step 2: Multiply the ten digits by the succeeding digit.

Step 3: Combine both the results.

Examples :

Multiply 27 by 23.

**Solution: **

The sum of unit digit is 10 = (7 + 3).

Multiply 3 by 7 = 3 × 7 = __21__

The digit in tens place is 2. The successor of 2 is 3.

Multiply 2 by 3 = 2 × 3 = __6__.

The solution is 621.

Multiplication of three digits number by a two digits number:

Examples :

Multiply 157 by 23.

**Solution: **

Multiplication of three digits number by a three digits number:

Examples :

Multiply 517 by 216.

**Solution: **

Therefore, 517 × 216 = 1,11,672.

Multiplication of three digits number by a three digits number when the ten digits and hundred digits are same and the sum of unit digit is 10:

Step 1: Multiply both the unit digits.

Step 2: Multiply the ten and the hundred digits by the succeeding digit.

Step 3: Combine both the results..

Examples :

Multiply 277 by 273.

**Solution: **

The sum of unit digit is 10 = (7 + 3).

Multiply 3 by 7 = 3 × 7 = __21__

The digit in tenths and the hundreds place is 27. The successor of 27 is 28.

Multiply 27 by 28 = 27 × 28 = __756__.

The solution is 75,621.

Multiplication Tricks by Numbers

Rule for Multiplying by 9:

- Multiply the number by 10.
- Subtract the number from product.

Examples 1:

Multiply 45 by 9

**Solution:**

Step 1: Multiply 45 by 10.

45 × 10 = 450

Step 2: Subtract 45 from 450.

450 – 9 = 405

Rule for Multiplying two digits number by 11:

Write the sum of the digits of the number in between the digits.

Examples 1:

Multiply 27 by 11

**Solution:**

Rule for Multiplying three digits number by 11:

Examples 2:

Multiply 157 by 11.

Solution: