A meadow (50 m long and 25 m wide) was investigated using the quadrat method. Swamp snowdrops were found in eight of the 20 investigated squares. Calculate the frequency (in %) of the marsh snowdrops in the studied meadow.

The patterns of relationships between organisms and between them and the environment are studied not only by observation but also by qualitative and quantitative methods.

The number of a population can be determined by quantitative methods:

1. Direct counting is used for populations with small numbers and inhabiting a limited territory.

2. The method of squares is used to determine the number of a population and to calculate its density mainly in grassy areas. A square frame with a certain area (0.25 m2 or 1 m ) is used. The frame is divided into equal squares by copper wire or wire.

3. Photography - used to determine the number of populations of large animals that live or gather in open spaces. Animals (large marine mammals, savannah animals, etc.) are filmed from a distance by helicopter or airplane.

4. Marking of individuals and recapture - used for isolated populations in cases where marked animals are well distributed among unmarked ones. A certain number of individuals from the population are captured, marked, and after repeated capture of animals from the same population, the number is calculated using the formula (number of individuals of the population = number of captured, marked and released individuals x total number of animals captured / number recaptured marked animals).​