Quantitative Aptitude Question on Sequence and Series

Question of The Day03-10-2019

If the 7^th term of an arithmetic progression is 7 and 11^th term of the same arithmetic progression is 21 then, what will be the 15^th term of the progression?

Answer

Correct Answer : a ) 35

Explanation :

For arithmetic progression, any n^th term is identified as

a_n=a+(n-1)*d

Where, a = 1^st term of the progression

a_n = n^th term of the progression

d = is the common difference

According to the question,

7^th term of the arithmetic progression is 7

So, a₇ = a + 6d = 7…….. (I)

11^th term of the arithmetic progression is 21

So, a₁₁ = a + 10d = 21……… (II)

Solving equation (I) and (II) for a and d, we get

a = – 14 and d=7/2

Thus, 15^th term of the progression will be

a₁₅ = a + 14d

a₁₅=-14+14*(7/2)=35

Hence, (A) is the correct answer.

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