Percentage
The concept of percentage is one of the most vital tools in mathematics for any competitive exam. The term 'percent' comes from the Latin phrase 'per centum,' which translates to 'by the hundred.' Essentially, a percentage is a way to express a number as a part of a whole that is divided into 100 equal pieces. For example, if you say that 40% of the students in a class are girls, it means that for every 100 students, 40 are girls.
Concepts (3)
This rule is used when the product of two items stays constant. A common example is 'Price x Consumption = Expenditure'.
This rule is used when the product of two items stays constant. A common example is 'Price x Consumption = Expenditure'. If the price of sugar increases, how much should you reduce eating to keep your total spending the same? If price increases by 25% (which is 1/4), the consumption must decrease by 1/(4+1) = 1/5 or 20% to keep the cost equal.
This concept measures how much a value has changed relative to its starting point. If a salary grows from 100 to 120, the increase is 20. To find the percentage, divide 20 by the original 100.
This concept measures how much a value has changed relative to its starting point. If a salary grows from 100 to 120, the increase is 20. To find the percentage, divide 20 by the original 100. Always use the 'Original Value' as the denominator (the bottom number) in your fraction. For example, if price falls from 50 to 40, the decrease is 10. The percentage decrease is (10/50) * 100 = 20%.
This applies when a value changes, and then that new value changes again. For example, a car price rises by 10% and then rises again by 20%. You cannot simply add them to get 30%. You must apply the second change to the updated price.
This applies when a value changes, and then that new value changes again. For example, a car price rises by 10% and then rises again by 20%. You cannot simply add them to get 30%. You must apply the second change to the updated price. A quick trick is to use the 'AB Formula' for two changes, where 'a' and 'b' are the percentage values. If a value decreases, use a minus sign.
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Start Lesson: Product Stability Rule