Given an A.P. whose terms are all positive integers. The sum of its first nine terms is greater than 200 and less than 220. If the second term in it is 12, then its 4th term is :
8
16
20
24
As we learnt in
Sum of n terms of an AP -
and
Sum of n terms of an AP
- wherein
first term
common difference
number of terms
given 200 < S9 < 220
and a+d=12 -----(i)
Then a+3d=?
Now 200 < 9(48 - 3a) <220
(because a is positive integer)
Option 1)
8
This option is incorrect
Option 2)
16
This option is incorrect
Option 3)
20
This option is correct
Option 4)
24
This option is incorrect
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