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Special Multiplication - 2 (Speed Math)

This method can be used to multiply two two-digit numbers under following conditions.

  • Units digits are same.
  • Sum of tens digits is $10.$

(Note: speed math calculator can be used to practise problems using this method.)

Example: Calculate 38 × 78

These are two digit numbers with same units digit $8.$ Also, sum of tens digits, $3$ and $7$ is $10.$ Therefore, we can use this special multiplication method.

Multiply tens digits and add common units digit to obtain left side of answer.

$3 × 7 + 8 = 29$

Multiply units digits to obtain right side of answer.

$8 × 8 = 64$

Combine left and right sides, that is, $29$ and $64$

Answer is $2964$

Example: Calculate 27 × 87

These are two digit numbers with same units digit $7.$ Also, sum of tens digits, $2$ and $8$ is $10.$ Therefore, we can use this special multiplication method.

Multiply tens digits and add common units digit to obtain left side of answer.

$2 × 8 + 7 = 23$

Multiply units digits to obtain right side of answer.

$7 × 7 = 49$

Combine left and right sides, that is, $23$ and $49$

Answer is $2349$

Example: Calculate 41 × 61

These are two digit numbers with same units digit $1.$ Also, sum of tens digits, $4$ and $6$ is $10.$ Therefore, we can use this special multiplication method.

Multiply tens digits and add common units digit to obtain left side of answer.

$4 × 6 + 1 = 25$

Multiply units digits to obtain right side of answer.

$1 × 1 = 1$

Right side must have two digits when using this method. So, write $1$ as $01$

Combine left and right sides, that is, $25$ and $01$

Answer is $2501$

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