Question

If a1=1/2×5, a2=1/5×8, a3=1/8×11,...,then a1, +a2, +a3, +....a100 is

• A. 25/151
• B. 1/2
• C. 1/4
• D. 111/55

Answer 1

The Correct Option is A

The correct answer is (A):
a1 = 1/2(5) = 1/3(1/2-1/5)
a2 = 1/5(8) = 1/3(1/5-1/8)
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a100 = 1/299(302) = 1/3(1/299-1/302)
All the terms like 1/5, 1/8,……..1/299 will cancel out.
∴ The sum = 1/3(1/2-1/302)
= 1/3(300)/(2)(302) = 50/302 = 25/151