FACTS AND FORMULAE FOR PERCENTAGE QUESTIONS
I.Concept of Percentage : By a certain percent , we mean that many hundredths. Thus x percent means x hundredths, written as x%.
To express x% as a fraction : We have , x% = x/100.
Thus, 20% = 20/100 = 1/5;
48% = 48/100 = 12/25, etc.
To express a/b as a percent : We have, .
II. If the price of a commodity increases by R%, then the reduction in consumption so as not to increase the expenditure is
If the price of the commodity decreases by R%,then the increase in consumption so as to decrease the expenditure is
III. Results on Population : Let the population of the town be P now and suppose it increases at the rate of R% per annum, then :
1. Population after n years =
2. Population n years ago =
IV. Results on Depreciation : Let the present value of a machine be P. Suppose it depreciates at the rate R% per annum. Then,
1. Value of the machine after n years =
2. Value of the machine n years ago =
V. If A is R% more than B, then B is less than A by
If A is R% less than B , then B is more than A by