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Question

The population of a town increased by 25% in the first year, then decreased by 20% in the second year and again increased by 10% in the third year. If the initial population was 50,000; find the population after 3 years.

This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is
55,000

Population Calculation After Percentage Changes

This problem requires calculating the final population after a series of percentage changes over three years, starting from an initial population.

Initial Population Value

The starting population of the town is given as 50,000.

Yearly Population Changes

The population dynamics over the three years are as follows:

  • Year 1: Population increased by 25%.
  • Year 2: Population decreased by 20%.
  • Year 3: Population increased by 10%.

Step-by-Step Population Calculation

We calculate the population at the end of each year sequentially:

  • End of Year 1: The population increases by 25%.

    The calculation is: \(P_1 = 50,000 \times (1 + \frac{25}{100}) = 50,000 \times (1 + 0.25) = 50,000 \times 1.25 = 62,500\)

  • End of Year 2: The population decreases by 20% from the Year 1 value.

    The calculation is: \(P_2 = 62,500 \times (1 - \frac{20}{100}) = 62,500 \times (1 - 0.20) = 62,500 \times 0.80 = 50,000\)

  • End of Year 3: The population increases by 10% from the Year 2 value.

    The calculation is: \(P_3 = 50,000 \times (1 + \frac{10}{100}) = 50,000 \times (1 + 0.10) = 50,000 \times 1.10 = 55,000\)

Combined Percentage Change Calculation

Alternatively, the final population can be found using a single combined calculation:

Final Population = Initial Population \(\times (1 + \text{Rate}_1) \times (1 - \text{Rate}_2) \times (1 + \text{Rate}_3)\)

Final Population = \(50,000 \times (1 + 0.25) \times (1 - 0.20) \times (1 + 0.10)\)

Final Population = \(50,000 \times 1.25 \times 0.80 \times 1.10\)

Final Population = \(50,000 \times (1) \times 1.10 = 55,000\)

Conclusion on Population After 3 Years

The population of the town after 3 years is 55,000.

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Similar Questions

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Important Questions from Percentage

  1. In an examination, 25% of the candidates failed in Mathematics and 12% failed in English. If 10% of the candidates failed in both the subjects and 292 candidates passed in both the subjects, which one of the following is the number of total candidates appeared in the examination?

  2. What is the value of 9% of 5500 + 2.4% of 1100 - 40% of 1600?

  3. Population of a village is 7960 in which 4660 are female. If in that village 60% are literate in which 70% female are literate, then what is the number of literate male ?

  4. The numbers of students of three classes of a school are in the ratio 4 : 5 : 6. If numbers of students in these classes increase by 25%, 20% and 25% respectively, then ratio of numbers of students will become:

  5. In an examination, Ram obtained 20 % more than Ashok but 10% less than Rajesh. If the marks obtained by Ashok is 1080. Then the Percentage marks obtained by Rajesh if the full marks is 2000 ;

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