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The number of plumbing repair jobs by Manji Plumbing Service in each of the last nine months in Nakuru town are listed below: Month---Jobs March 353 April 387 May 342 June...

      

The number of plumbing repair jobs by Manji Plumbing Service in each of the last nine months in
Nakuru town are listed below:
Month---Jobs
March 353
April 387
May 342
June 374
July 396
August 409
September 399
October 412
November 408
Required:
Required:
a)
i) Forecast the number of repair jobs Manji Plumbing Service will perform in December. Use the
least squares method.
Note:
manji1112029752.png
ii) What is your forecast for December using a three-period weighted moving average with weights of
0.6, 0.3, and 0.1. How does it compare with your forecast from part (i)
above? b)
i) What are the aims of time series analysis?
ii) Describe what a season is in the context of a time series and give some examples.
iii) Describe the stages in obtaining a time series trend using the method of semi averages.
iv) Why must forecasts be treated with caution?

  

Answers


Raphael
manji1112029752i.png
Note: June = 0.6 x 342 + 0.3 x 387 + 0.1 x 353
= 0.6 x May jobs + 0.3 x April jobs + 0.1 x March jobs
b)
i) Time series analysis is a method of studying the behaviour of variables changing with time. The
main aim is to come up with a given pattern to enable one forecast the variable in a future period.
ii) Season is a pattern formed within a given period over the trend (which is the general change over
time). For example the change from winter to summer in a given year will explain a season in
temperature readings / rain in any given year.
Another example is the consumption of alcohol during the month, starting a lot then reducing
during the mid-month and then increasing at end-month.
iii) The method of semi-averages uses two averages to obtain a trend from a given data. Firstly the
variable values are divided into two halfway. The first half number of variables are averaged and the
average put at the centre of them. Second half number variables are also averaged and the average
put at the centre of them.
Secondly, the trend line is drawn by joining the two average points.
iv) Forecasts must be treated with caution because of the following:
- Since historical data is used; it may not necessarily mean that is expected in the future.
- Furthermore, the extension cannot be pushed far ahead from the last historical data -Accuracy
reduces.
raphael answered the question on January 11, 2019 at 04:57


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