  Mathematical modelling for population growth leads to a differential
equation. In population growth model, we assume that rate increase of
population is proportional to current population. That is, dx / dt = kx, x is a
current population, k is proportionality constant represents growth rate. But
in real situation, it is often ambiguous to determine exact amount of current
population. It can be measured approximately. For instance, initially number of
bacteria is approximately 20 and this approximate number can be represented
using fuzzy number. Therefore, the appropriate growth or decay model is
described using fuzzy concept. With this motivation, this paper presents
solution of fuzzy growth and decay model. The solution is analysed using
Seikkala differentiability of fuzzy-valued function.
