Quantitative Aptitude – Sequence and Series – if a(base1)+a(base2)+a(base3)


Slot – 1 – Quantitative Aptitude – Sequence and Series – if a(base1)+a(base2)+a(base3)

if a(base1)+a(base2)+a(base3) – Video


Q. If a(base1)+a(base2)+a(base3)+….+ a(base n) = 3(2^(n+1) – 2), for every n≥1, then a(base11) equals ?

Answer: 6144

Solution: Given, a(base1)+a(base2)+a(base3)+ a(base4) + ………..+ a(base n) = 3*(2^(n+1) -2)
Put n =1
a(base1) = 3*(2^2 -2) = 6
Put n =2
a(base1)+a(base2) = 3*(2^3 -2) = 18
Or a(base2) = 12
Put n =3
a(base1)+a(base2)+a(base3) = 3*(2^4 -2) = 42
a(base3) = 42 – a(base2) – a(base1) = 42 – 12 – 6 =24
we can see that a1, a2 , a3 form a GP with common ratio 2 so
a(base11) = a(base1)*2^10 = 6*1024 = 6144

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