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Multiplication Multiplying Numbers with first digits sum 100 Speed Math

[Speed Math] MULTIPLYING NUMBERS WITH FIRST DIGITS SUM 100

Here’s an example of a SPEED MATH shortcut for MULTIPLYING NUMBERS WITH FIRST DIGITS SUM 100 : (Mul) F100dx from the MULTIPLICATION category.

Multiplying Numbers with first digits sum 100

When can I use this method?

For multiplying any 3-digit number with another 3-digit number such that the sum of the initial digits of the multiplier and multiplicand = 100 and the remaining digits of multiplier are same as that of the multiplicand.

For multiplying any 4-digit number with another 4-digit number such that the sum of the initial digits of the multiplier and multiplicand = 100 and the remaining digits of multiplier are same as that of the multiplicand.

You cannot use this method to multiply numbers with unequal number of digits, i.e. multiplying a 3-digit number with a 4-digit number.

 

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pdf Download Practice sheet for MULTIPLYING NUMBERS WITH FIRST DIGITS SUM 100

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Notes –

  1. Notice the way the common digits are added.
  2. When multiplying 3-digit numbers with common last digit, remember to write the RHS of the answer in 2-digit form by prefixing a zero, if the value is single digit, e.g. write ‘9’ as ‘09’.
  3. When multiplying 4-digit numbers with last 2 digits common, remember to write the RHS of the answer in 4-digit form by prefixing zero(s), if the value is less than 4-digit, e.g. write ‘9’ as ‘0009’ or ‘21’ as ‘0021’ or ‘121’ as ‘0121’.

Related Shortcuts –

Multiplying Numbers with first digits sum 10: (Mul) F10dx
Multiplying Numbers with first digits sum 1000: (Mul) F1000dx

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