A town has population of 20,000 in 1980. In one year i.e. by 1981 it increased by 25%. Next year i.e. in 1982, it decreased by 20%. The next year in 1983 there was an increase of 30%. What is the population at end of 1983?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 26000
Each change is a percentage of the population at the start of that year, so the changes are applied one after another, not added.
1981: \(20000+25\%=20000\times1.25=25000\)
1982: \(25000-20\%=25000\times0.8=20000\)
1983: \(20000+30\%=20000\times1.3=26000\)
Tip: Adding the percentages (\(25-20+30=35\%\)) would give 27000, which is wrong: a 25% rise followed by a 20% fall brings the number back to where it started.