Q. 293.6( 17 Votes )

The 4th term of an AP is 11. The sum of the 5th and 7th terms of this AP is 34. Find its common difference.

Answer :

Let a be the first term and d be the common difference.

Given: a4 = 11


a5 + a7 = 34


To find: common difference = d


Now, Consider a4 = 11


a + (4 - 1)d = 11


a + 3d = 11 ………….(1)


Consider a5 + a7 = 34


a + (5 - 1)d + a + (7 - 1)d = 34


2a + 10d = 34


a + 5d = 17 ……..(2)


Subtracting equation (1) from equation (2), we get,


2d = 6


d = 3


Common difference = d = 3


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