�ݺ�ߣ

Math can be terrifying for many people. This list
will hopefully improve your general knowledge
of mathematical tricks and your speed when you
need to do math in your head.

1. The 11 Times Trick
We all know the
trick when
multiplying by ten –
add 0 to the end of
the number, but did
you know there is
an equally easy trick
for multiplying a
two digit number by
11? This is it:
 Take the original number and imagine
a space between the two digits (in this
example we will use 52:
 5_2
 Now add the two numbers together
and put them in the middle:
 5_(5+2)_2
 That is it – you have the answer: 572.
 If the numbers in the middle add up to
a 2 digit number, just insert the second
number and add 1 to the first:
 9_(9+9)_9
 (9+1)_8_9
 10_8_9
 1089 – It works every time.

2. Quick Square
If you need to
square a 2 digit
number ending in 5,
you can do so very
easily with this trick.
 Multiply the first digit by
itself + 1, and put 25 on the
end. That is all!
 252 = (2x(2+1)) & 25
 2 x 3 = 6
 625

3. Multiply by 5
Most people
memorize the 5
times tables very
easily, but when you
get in to larger
numbers it gets
more complex – or
does it? This trick is
super easy.
 Take any number, then divide it by
2 (in other words, halve the
number). 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.
It works every time:
 2682 x 5 = (2682 / 2) & 5 or 0
 2682 / 2 = 1341 (whole number so
add 0)
 13410
 Let’s try another:
 5887 x 5
 2943.5 (fractional number (ignore
remainder, add 5)
 29435

4. Multiply by 9
This one is simple
– to multiple any
number between 1
and 9 by 9 hold both
hands in front of
your face – drop the
finger that
corresponds to the
number you are
multiplying
 (for example 9×3 – drop your
third finger) – count the
fingers before the dropped
finger (in the case of 9×3 it is
2) then count the numbers
after (in this case 7) – the
answer is 27.

5. Multiply by 4
This is a very simple
trick which may
appear obvious to
some, but to others
it is not.
 The trick is to simply
multiply by two, then
multiply by two again:
 58 x 4 = (58 x 2) + (58 x 2) =
(116) + (116) = 232

6. Calculate a Tip
If you need to leave
a 15% tip, here is the
easy way to do it.
 Work out 10% (divide the
number by 10) – then add
that number to half its value
and you have your answer:
 15% of $25 = (10% of 25) +
((10% of 25) / 2)
 $2.50 + $1.25 = $3.75

7. Tough Multiplication
If you have a large
number to multiply
and one of the
numbers is even,
you can easily
subdivide to get to
the answer:
 32 x 125, is the same as:
16 x 250 is the same as:
8 x 500 is the same as:
4 x 1000 = 4,000

8. Dividing by 5
Dividing a large
number by five is
actually very simple.
All you do is
multiply by 2 and
move the decimal
point:
 195 / 5
 Step1: 195 * 2 = 390
Step2: Move the decimal: 39.0
or just 39
 2978 / 5
 step 1: 2978 * 2 = 5956
Step2: 595.6

9. Subtracting from 1,000
To subtract a large
number from 1,000
you can use this
basic rule: subtract
all but the last
number from 9, then
subtract the last
number from 10:
 1000
-648
 step1: subtract 6 from 9 = 3
step2: subtract 4 from 9 = 5
step3: subtract 8 from 10 = 2
 answer: 352

 Multiply by 5: Multiply by
10 and divide by 2.
 Multiply by 6: Sometimes
multiplying by 3 and then 2
is easy.
10 and subtract the original
number.
10 and add twice the original
number.
3 and add 10 times original
number.
by 2.
7 and then multiply by 2
10 and add 5 times the
original number, as above.
 Multiply by 16: You can
double four times, if you
want to. Or you can multiply
by 8 and then by 2.
7 and add 10 times original
number.
20 and subtract twice the
original number (which is
obvious from the first step).

 Multiply by 19: Multiply
by 20 and subtract the
original number.
by 8 and then multiply by
3.
by 30 and subtract 3 times
the original number
(which is obvious from
the first step).
by 50 and subtract 5 times
the original number
(which is obvious from
the first step).
by 9 (as above) and put a
zero on the right.
by 100 and subtract twice
the original number.
by 100 and subtract the
original number.

 Find 7 % of 300. Sound Difficult?
 Percents: First of all you need to understand the word
“Percent.” The first part is PER , as in 10 tricks per listverse
page. PER = FOR EACH. The second part of the word is
CENT, as in 100. Like Century = 100 years. 100 CENTS in 1
dollar… etc. Ok… so PERCENT = For Each 100.
 So, it follows that 7 PERCENT of 100, is 7. (7 for each
hundred, of only 1 hundred).
8 % of 100 = 8. 35.73% of 100 = 35.73
But how is that useful??
 Back to the 7% of 300 question. 7% of the first hundred is 7.
7% of 2nd hundred is also 7, and yep, 7% of the 3rd hundred
is also 7. So 7+7+7 = 21.
 If 8 % of 100 is 8, it follows that 8% of 50 is half of 8 , or 4.

 Break down every number that’s asked into
questions of 100, if the number is less then 100,
then move the decimal point accordingly.
 EXAMPLES:
8%200 = ? 8 + 8 = 16.
8%250 = ? 8 + 8 + 4 = 20.
8%25 = 2.0 (Moving the decimal back).
15%300 = 15+15+15 =45.
15%350 = 15+15+15+7.5 = 52.5
 Also it’s useful to know that you can always
flip percents, like 3% of 100 is the same as 100%
of 3.
 35% of 8 is the same as 8% of 35.

�ݺ�ߣ

10 easy arithmetic tricks

More Related Content

10 easy arithmetic tricks