Question

If the sum of 4 consecutive terms of an AP is 36, then arithmetic mean of these terms in the AP is A)9 B)12 C)18 D)can't be determined

Answer 1

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let the ap of 4 terms be :

a -3d , a-d , a+d , a+3d

where a1 = a-3d

where d = 2d

The it is given that sum of the terms ;

a -3d + a-d + a+d + a+3d = 36

4a = 36

a = 9

then arithmatic mean = sum of observations/number of observations

= (a-3d+a-d+a+d+a+3d)/4

= 4a/4

= a = 9