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Percentage

Aptitude

Percentage -> IMPORTANT FACTS AND FORMULAE

Concepts 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.
To express a/b as a percent : we have, a/b = (a/b×100)% .
Results on population : Let the population of a town be P now and suppose it increases at the rate of R% per annum, then :
Population after n years = P[1+R/100]n.
Population n years = p / [1+R/100]n.

Percentage -> SOLVED EXAMPLES

1. Express each of the following as a decimal.
28%
  Sol. = 28/100 = 0.28%.
2. Express each of the following as a decimal.
0.04%
  Sol. = 0.04/100 = 0.0004%.
3. Express each of the following as a fraction.
4%
  Sol. = 4/100 = 1/25.

Percentage -> EXERCISE

13. Of the 1000 inhabitants of a town, 60% are males of whom 20% are literate. If, of all the inhabitants, 25% are literate, then what percent of the females of the town are literate?
 
  • A. 22.5
  • B. 27.5
  • C. 32.5
  • D. 37.5
Ans: C.
Sol.
Number of males = 60% of 1000 = 600.
Number of females = (1000-600) = 400.
Number of literates = 25% of 1000 = 250.
Number of literate males = 20% of 600 = 120.
Number of literate females = (250 - 120) = 130.
∴ Required percentage = (130 / 400 x 100)% = 32.5%.
 
14. 45% of 750 - 25% of 480 = ?
 
  • A. 216
  • B. 217.50
  • C. 236.50
  • D. 245
Ans: B.
Sol.
Given expression = (45/100 x 750) - (25/100 x 480)
= (337.50 - 120)
= 217.50
 
 
15. The current birth rate per thousand is 32, whereas corresponding death rate is 11 per thousand. The net growth rate in terms of population increase in percent is given by
 
  • A. 0.0021%
  • B. 0.021%
  • C. 2.1%
  • D. 21%
Ans: C.
Sol.
Net growth on 1000 = (32 - 11) = 21.
Net growth on 100 = (21/1000 × 100)% = 2.1 %.