Find the harmonic mean of 2 and 4.
Answer: B
The harmonic mean (H.M.) of n numbers is the reciprocal of the arithmetic mean of their reciprocals.
For two numbers a and b, H.M. = \(\frac{2}{\frac{1}{a} + \frac{1}{b}} = \frac{2ab}{a+b}\).
H.M. = \(\frac{2 \times 2 \times 4}{2+4} = \frac{16}{6} = \frac{8}{3}\).