ANSWER:

YEAR: 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Values: 242 250 252 249 253 255 251 257 260 265 262

To find:

3-yearly average

Explanation:

\displaystyle Average = \frac{Sum \ of\ terms }{\ Total \ no \ of \ terms}Average=

Total no of terms

Sum of terms

1) Average of years 1990, 1991, 1992:

\begin{gathered}\displaystyle { a_1 = \frac{242 +250 + 252}{3} }\\\\\displaystyle a_1 = 248\end{gathered}

a

1

=

3

242+250+252

a

1

=248

2) Average of years 1993, 1994,1995 :

\begin{gathered}\displaystyle a_2 = \frac{249+253+255}{3} \\\\\displaystyle a_2 = 252.33\end{gathered}

a

2

=

3

249+253+255

a

2

=252.33

3) Average of years 1996, 1997, 1998:

\begin{gathered}\displaystyle a_3 = \frac{251+257+260}{3}\\\\ \\\displaystyle a_3 = 256\end{gathered}

a

3

=

3

251+257+260

a

3

=256

4) Average of years 1999, 2000:

\begin{gathered}\displaystyle a_4 = \frac{265+262}{2} \\\\\displaystyle a_4 = 263.5\end{gathered}

a

4

=

2

265+262

a

4

=263.5

The above data SHOWS that the average data is increased by 3-yearly.