Yves S. answered 02/06/20
Statistics made easy for undergrad, grad and MBA students
L(t) = alpha*F(t) + (1-alpha)*(L(t-1)+T(t-1))
T(t) = beta*(L(t)-L(t-1))+(1-beta)*T(t-1)
Forecast = Level + Trend
L(t=1) = 120; T(t=1) = 60
L(t=2) = 190; T(t=2) = 0.3*(190-120)+(1-0.3)*60 = 63
Similarly:
L(t=3) = 0.5*150+(1-0.5)*(190+63) = 201.5 = 202
T(t=3) = 0.3*(201.5-190)+(1-0.3)*63 = 47.55 = 48
Hope that helps!