The population growth rate can be obtained using the formula:
P = Po*e^(rt), where
P = final number of population
Po = initial number of population
r = rate of growth
t = time
For this case, the unknown variable is r or the rate of growth. The initial number of the population 1000, and by the end of 1 year, it is equal to 1000 + (15-35) which is equal to 980. Thus, the equation would be 980 = 1000*e^(r*1). The population growth rate would then be -2.02%. The negative growth rate is due to the decrease in population from 1000 to 980.