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Fill in the blank with either “directly” or “inversely”.


(1)    Area of a square: A=s2

A is proportional to s.

(2)    Average speed: r=d/t

R is proportional to t.

(3)    Surface area of a cube: S=6r2

S is proportional to r.

(4)    Free vibrations:

 is proportional to W.