Answer :

(a)Population density of a fish in a lake can be measured by the number of fish per trap in the lake.

(b)Total frogs present in the pond = 100 frogs

Number of frog births per year = 20

Birth rate of the population=

Number of frog births per year/ Total population of frogs

20 / 100 = 0.2 off springs per year


The three types of age pyramids are Expanding, Stable and declining.

Stable age pyramid is also known as ‘bell shaped’ pyramid. In this type of pyramid the pre and post reproductive population is the same. The population remains unchanging, neither declining nor growing. The example of such population is USA.

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