In the past Judy Holmess tire dealership sold a n average of

In the past, Judy Holmes’s tire dealership sold a n average of 1,1 00 ra dials each year. In the past three years, 242, 249 and 245 , respectively, were sold in fall, 3 21, 323 and 329 in winter, 2 08, 190 and 204 in spring, and 3 29, 338 and 322 in summer. With a major expansion planned, Judy projects sales next year to increase to 1, 6 00 radials. What will the demand be each season?

Solution

The data is first entered in an spreadsheet. The following R program gives the forecast:

sales <- read.csv(\"clipboard\",header=F)

v2 <- ts(V1,freq=4)

v2stl <- stl(v2,s.window=\"periodic\")

library(forecast)

forecast(v2stl,h=4)

The forcast for the forthcoming fall, winter, spring, and summer is

> forecast(v2stl,h=1)
Point Forecast Lo 80 Hi 80 Lo 95 Hi 95
4 Q1 245.0168 237.9285 252.1050 234.1762 255.8574