Quantitative Aptitude – Algebra – Functions – If f(x + 2) = f(x) + f(x + 1)

Slot -1 – Quantitative Aptitude – Algebra – Functions – If f(x + 2) = f(x) + f(x + 1)

 If f(x + 2) = f(x) + f(x + 1) for all positive integers x, and f(11) = 91, f(15) = 617, then f(10) equals?
Answer: 54

Solution:

Given , f(x + 2) = f(x) + f(x + 1)
f(15) = f(13) + f(14)
f(13) + f(14) = 617 —————1)
f(12) + f(13) = f(14) ————-2)
f(11) + f(12) = f(13)————-3)
from eq 1) , 2) & 3)
2f(11) + 3f(12) = 617
Putting f(11) = 91
f(12) = (617 – 2*91)/3 = 145
f(12) = f(11) + f(10)
so f(10) = f(12) – f(11) = 145 – 91 =54
Answer: 54

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