If in a pond there were 20 lotus plants last year and through reproduction 8 new plants are added, taking the current population to 28, then the birth rate will be -
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 0.4 offspring per lotus per year
The birth rate of a population is a per capita rate. It is the number of new individuals born during a period, divided by the number of individuals present at the start.
Birth rate = number of births ÷ starting population
Births = 28 − 20 = 8 new plants; starting population = 20 plants
Birth rate = 8 ÷ 20 = 0.4 offspring per lotus
The new plants were added between last year and now, so the time unit is per year.
Option (1) 0.1 offspring per lotus per month — Incorrect. Both parts are wrong. 8 ÷ 20 is 0.4, not 0.1, and the data cover a year, not a month.
Option (2) 0.4 offspring per lotus per day — Incorrect. The number is right but the time unit is wrong. The 8 plants were added over a year, not in a day.
Option (3) 0.1 offspring per lotus per year — Incorrect. The time unit is right but the number does not follow from the data. 8 births in 20 plants give 0.4.
Option (4) 0.4 offspring per lotus per year — Correct. Birth rate is the number of births per individual in a given period. 8 new plants ÷ 20 plants = 0.4 offspring per lotus per year.
Note: A similar question was also asked in CUET (UG) 2025 on 16-05-2025 (Slot 1) and on 15-05-2025 (Slot 1).
NCERT Extract:
Population Attributes – …
