Interview Question: Sum It Up

Sample Question #69 (mathematics)

Solve

a0 + a1 + a2 + a3 + … + an

where n is a natural number and n > 1.

Similar question: what if n is infinity?

(Hint: solve the infinity case first)

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One Response to Interview Question: Sum It Up

  1. Brett says:

    I’ll give you the answer for when n is infinity.
     
    Write  s = a0 + a1 + a2 + a3 + … .  Multiply both sides by a, then subtract the two equations.  As you get the final formula, you need to explain what condition a must satisfy for s to make sense.  For example, if a>=1, the sum goes to infinity!  Now, what if a=-0.2?
     
    To solve the first question, you need to do a little deduction (hint: start summing at n+1).  Shouldn’t be difficult.

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