Question

A set of 20 tuning forks is arranged in a series of increasing frequencies. If each fork gives 4 beats with respect to the preceding fork and the frequency of the last fork is twice the frequency of the first, then the frequency of last fork is _______ Hz

Answer 1

The correct answer is 152 Hz
f1 = f , f2 = f + 4
f3 = f + 2 × 4 , f4 = f + 3 × 4
f20 = f + 19 × 4
= f + (19 × 4) = 2 × f
f = 76 Hz.
Frequency of last tuning forks = 2f
= 152 Hz