Percentage Maths Trick, Question with solution
PERCENT
The word percent means “divided by hundred”. The word percent come from “Per Centum” The word centum means hundred.
Percent means ” out of 100″ . we use the percent symbol is %.
A percent can always be written as a decimal, and a decimal can be written as a percent, by moving the decimal point two places to the right like this;
0.75= 75%
Here are three ways to write the same thing:
0.75=75%=75/100
We can find any percent of a given number by changing the percent to a decimal and multiplying.
Lets’s find 20 percent of 400
First change 20% to a decimal by moving the decimal point 2 places to the left.
20%= 0.20
Then multiply,
0.20*400=80
20% of 400 is 80
MENTAL MATH
There’s an easy way to find 10% of a number without multiplying. just move the decimal point in the number left by one place.
Let’s try bit with these number:
456,76,56457
10% of 456= 45.6
10% of 76= 7.6
10 % of 56457= 5645.7
APPLY LITTLE PRESENCE OF MIND AND CALCULATE PERCENTAGE AS FAST AS YOU CAN:
Example:
Que: 24 is 6% of what number?
Ans: 24=6%*n
n= 24/6%
n= 400
PERCENT INCREASE AND DECREASE
We need to find the percent of increase or decrease in a given quantity. to find this calculate the increase and divided it by the original amount.
This can be represented as
Percent increase of a quantity= (Actual increase/ original Amount)* 100%
Percent decrease of a quantity=( Actual decrease/ original Amount)*100%
Generalising this , we can write as
Percent of change= (Amount of change/Original amount)*100%
SOME COMMON PERCENTS AND THEIR FRACTIONAL EQUIVALENTS: 
EXAMPLE:
Question: Mohit bought a new car in 1995 for 10,000rs in 2000 the car was priced at 18,500. Calculate the percentage increase in the car over the five years.
10,000+(a% of 10,000) = 18,500
Hence a% of 10000= 8,500
Using the formula:
10,000* a/100= 8500
100a=8500
a=8500/100=85%
CONVERSION OF DECIMAL, FRACTION & PERCENT
Decimal to Fraction
ab.cde= (10a)+b+(c/10)+(d/100)+(e/1000)
=abcde/1000
Fraction to decimal
Divided the numerator by the denominator.
3/7= 0.4285
Decimal to percent
Move the decimal points two places to the right
0.36= 36%
Fraction to percent
Divided the numerator by the denominator. then move the decimal point places to the right.
3/7= 42.85%
CONVERSION OF DECIMAL INTO FRACTIONS
STEP 1.
Count the number of decimal places.
Ex. 0.445 (three decimal places)
STEP 2.
Find the denominator of the fraction using the following table.
STEP 3.
Write the decimal digits without the decimal point as the numerator.
445/1000
STEP 5.
Reduce the fraction to its lowest term.
445/1000=89/200
EXAMPLE:
Que: If result of increasing by 300% of a is b, then a is what percent of b?
Ans:
Here is given that a is increased by 300% of a
Now, 300% of a= 3a
If 3a is added to a, then result of increase in a
=a+3a
=4a
It is given that the result of increases is equal to b.
4a=b
a=b/4
Now 1/4=25%
a=25% of b.
Check also: Basics of Simple Interest & Compound Interest (SI and CI Basic concept)