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Question
The first three terms of an AP respectively are 3y – 1, 3y + 5 and 5y + 1. Then y equals:
(A) –3
(B) 4
(C) 5
(D) 2
Solution
The first three terms of an AP are 3y – 1, 3y + 5 and 5y + 1 respectively
We need to find the value of y.
We know that if a, b and c are in AP, then:
b − a = c − b ⇒ 2b = a + c
∴2(3y+5) = 3y − 1 + 5y + 1
⇒6y + 10 = 8y
⇒10 = 8y −6y
⇒2y = 10
⇒y = 5
Hence, the correct option is C.
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