Foundation
Mathematics Foundation
Sum of n terms of an AP
Question

The 13th term of an AP is 4 times its 3rd term. If its 5th term is 16 then the sum of its first ten terms is

135

175

150

160

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Solution

T13 = 4 × T3 ⇒ a + 12d = 4(a + 2d) ⇒ 3a – 4d = 0.                ....(i)

T5 = 16 ⇒ a + 4d = 16.                                                           ....(ii)

On Solving (i) and (ii), we get a = 4 adn d = 3.

S10=102(2a+9d)=5(2×4+9×3)=175