DIVIDE AND CONQUER

My Dear Aunt Sally (MDAS) or Multiplication, Division, Addition, Subtraction (MDAS), I heard this first from my father.

This means that when you are given a bunch of  numbers that involve all the arithmetic operations, the sequence should be as follows:

Multiplication (M), Division (D), Addition (A) and Subtraction (S).
This explains why I started showing some samples of tricks in Multiplication first.

Fingering Is Actually Fun

For those who have children or grandchildren who are just starting to master or memorize the multiplication tables, I learned that most often, verifying the product by using one’s ten fingers is quite reliable and fun.

A good example is multiplying any single digit number (1-9) by 9:

a.      9 x 4
Answer: 36

Hand verification: Hold both hands in front of your face – drop the finger that corresponds to the number you are multiplying (4) meaning the (4th finger) – count the fingers before the dropped finger (in this case of 9 x 4) it is 3), then count the number after (in this case 6) – the answer is 36.

b.      9 x 6

Answer: 54

Hand verification: Hold both hands in front of your face – drop the finger that corresponds to the number you are multiplying (6) meaning the (6^th finger) – count the fingers before the dropped finger (in this case it is 5), then count the number after (in this case 4) – the answer is 54.

DIVIDE and CONQUER

Dividing numbers by 5:

Examples:

195 / 5 =

Answer: 39

How: Multiply the number (195) by 2 and move the decimal point:

Step1: 195 * 2 = 390 


Step2: Move the decimal: 39.0 or just 39

2978 / 5 =

Answer: 595.6

How: Multiply the number (2978) by 2 and move the decimal point:

step 1: 2978 * 2 = 5956


Step2: 595.6

Dividing by 25

Example:

 1820 / 25 =

Answer: 72.8

How:  1820 x 4/100* = 7280/100 = 72.80

*Note: 1/25 = 4/100

 DIVIDE AND CONQUER

My Dear Aunt Sally (MDAS) or Multiplication, Division, Addition, Subtraction (MDAS), I heard this first from my father.
This means that when you are given a bunch of  numbers that involve all the arithmetic operations, the sequence should be as follows: Multiplication (M), Division (D), Addition (A) and Subtraction (S).
This explains why I started showing some samples of tricks in Multiplication first.
Fingering Is Actually Fun
For those who have children or grandchildren who are just starting to master or memorize the multiplication tables, I learned that most often, verifying the product by using one’s ten fingers is quite reliable and fun.
A good example is multiplying any single digit number (1-9) by 9:

a.      9 x 4

Answer: 36

Hand verification: Hold both hands in front of your face – drop the finger that corresponds to the number you are multiplying (4) meaning the (4th finger) – count the fingers before the dropped finger (in this case of 9 x 4) it is 3), then count the number after (in this case 6) – the answer is 36.

b.      9 x 6

Answer: 54

Hand verification: Hold both hands in front of your face – drop the finger that corresponds to the number you are multiplying (6) meaning the (6^th finger) – count the fingers before the dropped finger (in this case it is 5), then count the number after (in this case 4) – the answer is 54.

DIVIDE and CONQUER

Dividing numbers by 5:

Examples:

195 / 5

Answer: 39

How: Multiply the number (195) by 2 and move the decimal point:

Step1: 195 * 2 = 390 


Step2: Move the decimal: 39.0 or just 39

2978 / 5 =

Answer: 595.6

How: Multiply the number (2978) by 2 and move the decimal point:

step 1: 2978 * 2 = 5956


Step2: 595.6

Dividing by 25

Example:

 1820 / 25 =

Answer: 72.8

How:  1820 x 4/100* = 7280/100 = 72.80

Note: 1/25 = 4/100