Answer 1

Construct the following table for finding 4-yearly centred moving averages:

Year t	Percentage of Enrolment  yt	4–yearly moving total	4–yearly moving average	2 unit moving total	4–yearly centred moving averages trend value
1960	0
1965	3
		10	2.5
1970	3			6	3
		14	3.5
1975	4			7.5	3.75
		16	4
1980	4			8.75	4.375
		19	4.75
1985	5			10.5	5.25
		23	5.75
1990	6			12.5	6.25
		27	6.75
1995	8			14.75	7.375
		32	8
2000	8
2005	10				4.5