Mental Maths
Mental 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 problemsolving ability in children.
 Regular practice of mental sums improves the child sense in numbers.
Multiplication Tricks
Multiplication of a whole number with the multiples of 10:
 Multiply the nonzero part of both the factors.
 Count the number of zeros in each of the factor.
 Add the same number of zeros in the product.
Example 1:
Multiply 2100 by 400.
Solution:
Step 1: Multiply 21 by 4
21 Ã— 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 Ã— 4 = 8,40,000.
Example 2:
Multiply 100 by 1000.
Solution:
Step 1: Multiply 1 by 1
1 Ã— 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 Ã— 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.
Example:
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.
Example:
Multiply 27 by 23.
Solution:
The sum of unit digit is 10 = (7 + 3).
Multiply 3 by 7 = 3 Ã— 7 = 21
The digit in tens place is 2. The successor of 2 is 3.
Multiply 2 by 3 = 2 Ã— 3 = 6.
The solution is 621.
Multiplication of three digits number by a two digits number:
Example:
Multiply 157 by 23.
Solution:
Multiplication of three digits number by a three digits number:
Example:
Multiply 517 by 216.
Solution:
Therefore, 517 Ã— 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.
Example:
Multiply 277 by 273.
Solution:
The sum of unit digit is 10 = (7 + 3).
Multiply 3 by 7 = 3 Ã— 7 = 21
The digit in tenths and the hundreds place is 27. The successor of 27 is
28.
Multiply 27 by 28 = 27 Ã— 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.
Example 1:
Multiply 45 by 9
Solution:
Step 1: Multiply 45 by 10.
45 Ã— 10 = 450
Step 2: Subtract 45 from 450.
450 â€“ 9 = 405
Rule for Multiplying two digits number by 11:
Write the sum of the digits of the number in between the digits.
Example 1:
Multiply 27 by 11
Solution:
Rule for Multiplying three digits number by 11:
Example 2:
Multiply 157 by 11.
Solution: