16Hit1600
Advanced MathVery hardDifference of inputs from a ratio of outputs

Advanced Math practice question

The function f is defined by f(x) = 3ˣ. If f(a) = 27·f(b), what is the value of a − b?

Answer: 3

3ᵃ = 27·3ᵇ = 3³·3ᵇ = 3^(b + 3), so a = b + 3 and a − b = 3.

Common wrong answers

If you answered 9
9 is 3², from misreading 27 as 3².
If you answered 27
27 is the ratio of the outputs, not the difference of the inputs.
If you answered -3
−3 has the difference the wrong way round.

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