The 4th and 7th term of an arithmetic progression are 11 and -4 respectively. What is the 15th term?
A. -49 B. -44 C. -39 D. -34 Answer: Option BShow Answer
Solution(By Apex Team)
Let the first term of an AP = a and the common difference = d
4th term of AP = A4 = a + 3d =11 ……(1)
7th term = A7 = a + 6d = -4 ……(2)
Subtracting equation (1) from (2), we get :
⇒ 6d – 3d = -4 -11
⇒ 3d = -15
⇒ d = $\Large\frac{-15}{3}$ = -5
Substituting it in equation (1)
⇒ a = 11 – 3(-5) = 11 + 15 = 26
∴ 15th term = A15 = a + 14d
= 26 + 14(-5)
= 26 – 70
= -44
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