Two strings A and B have equal lengths and are made of the same material. String A has twice the diameter of string B. Both strings are stretched separately between identical rigid supports with the same tension.
(i) Obtain the ratio of the linear mass densities μA:μB of the two strings.
(ii) Deduce the ratio of their fundamental frequencies fA:fB.
(iii) If the fundamental frequency of string B is 400Hz, calculate the lowest frequency at which both strings can vibrate simultaneously without producing beats.