COMPOUND INTEREST - Easy Method
You can calculate compound interest mentally
Question
========
Find the compound interest on Rs 2500 @ 12% P.A. for two years
Step 1 First we add rates Let it be A
Step 2 Multiply rates and divide by 100 Let it be B
Step 3 Add A and B It is our compound interest rate percentage for two years .Take percentage
12 + 12 + ( 12+ 12 ) / 100 = 24 + 1.44 = 25.44
Find 25.44 % of 2500
and that is compound interest
Easy Method of Finding %
====================
(25 / 100)x 2500 + (44/10000)x2500 = 625 + 11
625 + 11 =636
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Rs 636 is our compound interest
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Total amount = 2500 + 636 = 3136
ADDITION OF TIMES
Now you want to add these two numbers together:
135
355
____
490
So we now have a sub total of 490. What you need to do to this and all sub totals is add the time constant of 40.
No matter what the hours and mins are, just add the 40 time constant to the sub total.
490 + 40 = 530
So we can now see our answer is 5 hrs and 30 mins!
Eg 2
========
Time 1: 1 hr 35 min
Time 2 : 2 hr 45 min
Time 3 : 4 hr 25 min
ADD
****
135
245
425
------
805
add constant 40
805+40 = 845
so, total time is 8 hrs 45 mins
Multiply large number by 5
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 everytime:
2682 x 5 = (2682 / 2) & 5 or 0
2682 / 2 = 1341
(whole number so add 0)
13410
Let’s try another:
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5887 x 5
2943.5
(fractional number
(ignore remainder, add 5)
29435
Multiply by 9 – with your fingers
Multiply by 9 – with your fingers
===========================
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.
Tough Multiplication- Made Easy
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
Dividing by 5
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:
Eg1
=========
195 / 5
Step1: 195 * 2 = 390
Step2: Move the decimal: 39.0 or just 39
Eg2
===========
2978 / 5
step 1: 2978 * 2 = 5956
Step2: 595.6
Assorted Multiplication Rules
Assorted Multiplication Rules
============================
Multiply by 5: Multiply by 10 and divide by 2.
Multiply by 6: Sometimes multiplying by 3 and then 2 is easy.
Multiply by 9: Multiply by 10 and subtract the original number.
Multiply by 12: Multiply by 10 and add twice the original number.
Multiply by 13: Multiply by 3 and add 10 times original number.
Multiply by 14: Multiply by 7 and then multiply by 2
Multiply by 15: Multiply by 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.
Multiply by 17: Multiply by 7 and add 10 times original number.
Multiply by 18: Multiply by 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.
Multiply by 24: Multiply by 8 and then multiply by 3.
Multiply by 27: Multiply by 30 and subtract 3 times the original number (which is obvious from the first step).
Multiply by 45: Multiply by 50 and subtract 5 times the original number (which is obvious from the first step).
Multiply by 90: Multiply by 9 (as above) and put a zero on the right.
Multiply by 98: Multiply by 100 and subtract twice the original number.
Multiply by 99: Multiply by 100 and subtract the original number.
Percentages Made Easy
Percentages
=============
Find 7 % of 300. Sound Difficult?
Percents:
First of all you need to understand the word “Percent.”
The first part is PER , . 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% of 200 = ? 8 + 8 = 16.
8% of 250 = ? 8 + 8 + 4 = 20.
8% of 25 = 2.0 (Moving the decimal back).
15% of 300 = 15+15+15 =45.
15%350 = 15+15+15+7.5 = 52.5
Also it’s usefull 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.
check divisibility by 7
The known rules for testing for divisibility by 7 are amazingly cumbersome.
Here's one such rule.
To find out if a number is divisible by 7,
double the last digit,
then subtract it from the remaining digits of the number.
If you get an answer divisible by 7, then the original number is divisible by 7.
If you don't know whether the new number is divisible by 7, you apply the rule again.
For example,
=========
to check whether 616 is divisible by 7,
double the last digit (6 x 2 = 12),
then subtract the answer from the remaining digits (61 – 12 = 49).
Because 49 is divisible by 7, so is 616.
The method works quite well for small numbers. For larger numbers,
the rule is sufficiently complicated that it takes nearly as much effort
to check for divisibility as it would be to perform the division
operation itself.
HERE IS ANOTHER METHOD:
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• Consider the following multiple of 7:
6,049,344
• Separate the number into pairs of digits, starting from the right.
6 04 93 44
• Calculate the difference between each pair of digits and the
nearest upper or lower multiple of 7, beginning with the first pair at
the right. For the first pair, use the lower multiple, for the second
use the upper multiple, for the third use the lower multiple, and so on.
44 – 42 = 2; 98 – 93 = 5; 04 – 0 = 4; 7 – 6 = 1
• Write out the resulting digits in the order in which they were calculated.
2541
• Repeat the process on the digits 2541.
25 41
41 – 35 = 6; 28 – 25 = 3
63
• The final pair, 63, is a multiple of 7. Hence, the original number must also be a multiple of 7
