A shrink by a factor of Two-fifths [image 1] for the exponential decay function f(x)= a (two-ninths) Superscript x [image 2] occurs when a =[___].

In f(x) = a(2/9)^x, the coefficient a multiplies every output value, so it sets the vertical scale. A shrink by a factor of 2/5 means a = 2/5. Therefore, the correct choice is B, 2/5.

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