“Mastering the three Rs (Reading, ‘Riting, and ‘Rithmetic is
mastering the tools to acquire knowledge and to survive day to day life.
Learning and loving them leads to living a fruitful and fearless future.”
I learned this from my late father, Antonio B. Maynigo – a
schoolteacher, Principal, and District Supervisor.
Following his advice, I got interested and tried to be
proficient in all three fundamentals. Reading helped me to self-study while
engaging in extra-curricular activities including sports, which I loved. It
also helped me expand my knowledge base both in non-fiction and fiction reading
materials. The latter, of course, also served as entertainment.
Writing facilitated the development of my confidence in expressing
myself both orally, and in writing. It taught me the art of communication. This
proficiency allowed me the privilege of ghostwriting the speeches of a couple
of Philippine Senators, Cabinet Secretaries, and business executives.
Arithmetic or Mathematics can be terrifying for many people.
This is why my father advised early exposure to numbers. Kids must learn to
love not fear them. Most of the time, some tricks or shortcuts that would
impress other kids, would motivate them to learn Math and take it seriously.
This was what happened to me. My father taught me some shortcuts
or mental math. Knowing them helped develop my liking of numbers. I will give a
few examples and, later on, I’ll write a series to teach our readers these
mental math tricks or skills. Adult readers of this column who have children or
grandchildren may be interested in learning and showing them to the latter.
Go Forth and Multiply
I will start by giving some examples in mental computation
in multiplication. My sources include my late father and some published materials.
Examples:
1. Squaring or
multiplying a 2-digit number ending in 5 by itself.
a. 25 x 25 =
Answer: 625
How:
Multiply the first number (2) by the next higher number (3) and attach 25.
2 x 3 = 6, then attach 25 = 625
b. 35 x 35 =
Answer: 1225
How:
Multiply the first number (3) by the next higher number (4) and attach 25.
3 x 4 = 12, then attach 25 = 1225.
2. Multiplying any 2-digit number by 11.
a. 72 x 11 =
Answer: 792
How:
The product begins and ends with the two numbers (7 and 2). The number in the
middle is the sum of the two numbers (7+2) = 9. So, beginning number (7),
middle number (9) and ending number (2) you get = 792
b. 53 x 11 =
Answer: 583
How:
The product begins and ends with the two numbers (5 and 3). The number in the
middle is the sum of the two numbers (5+3) = 8. So, beginning number (5),
middle number (8) and ending number (3) you get = 583
3. Multiplying by 5
a. 8624 X 5 =
Answer: 43120
How:
Take the number (8624), divide it by 2, If the result is whole, add a 0 at the
end. If it is not, ignore the remainder and add a 5 at the end.
8624/2 = 4312 (whole number so add 0)
43120
b. 5887 x 5 =
Answer:
29435
How:
Take the number (5887), divide it by 2. If the result is whole, add a 0 at the
end. If it is not, ignore the remainder and add a 5 at the end.
5887/2 = 2943.5 (ignore remainder, add 5)
29435
4. Multiplying 2-digit numbers by a single digit number
a. 53 x 8 =
Answer: 424
How:
First multiply 50 by 8, multiply 3 by 8, then, add the product of both.
50 x 8 = 400
3 x 8 = 24
424
b. 72 x 5 =
Answer: 360
How: First
multiply 70 by 5, multiply 2 by 5, then add the product of both.
70 x 5 = 350
2 x 5 = 10
360
The above are all mental computations –
no paper and pencil are used. Practice makes perfect. So, if done often, one
could develop real mental math skills.
I will provide more examples on mental math involving addition, subtraction, division and multiplication in subsequent columns.
The next will most likely be entitled, “Divide and Conquer”. J
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