Problem: A harmonic progression is a sequence of numbers such that their reciprocals are in arithmetic progression. Let Sn​ represent the sum of the first n terms of the harmonic progression; for example, S3​ represents the sum of the first three terms. If the first three terms of a harmonic progression are 3,4,6, then:
Answer Choices:
A. S4​=20
B. S4​=25
C. S5​=49
D. S6​=49
E. S2​=1/2S4​
Solution:
31​,41​,161​,121​,0 with d=−121​
therefore the terms of the H.P. are 3,4,6,12 only ∴S4​=25