A sequence x1 , x2 and x3 … is said to be in a harmonic progression if the reciprocals 1/x1,1/x2
and 1/x3 are in arithmetic progression. The 5th term and the 7th term for an harmonic progression are 30
and 50 respectively. What is the difference between the 6th and 4th term.
a. 16 b. 14.5 c. 13.4 d. 12.5.

• a/1+4d = 30
  => a = 30 + 120d
  
  Also, a/1+6d = 50
  => a = 50 + 300d
  
  Thus, d = -20/180 = -1/9 and, a = 50/3
  
  => 4th Term = 50/2 = 25.
  6th Term = 50*3/4 = 75/2 = 37.5
  
  Thus, Difference = 12.5
• 12 years agoHelpfull: Yes(12) No(0)
• 12.5 is answer
  
• 12 years agoHelpfull: Yes(4) No(0)