The monthly salary of a person was Rs 320 for each of the first 3 years. He next got annual increment of Rs 40 per month for each of the following successive 12 years.His salary remained stationary till retirement when he found that his average monthly salary during his service period was Rs 694. Find the period of his service?
a > 25
b> 15
c> 40
d> 50

• total salary for first 3years=3*12*320=11520
  rs 40 per month increment for each of following 12 consecutive years.
  for 4th year monthly salary=rs 360
  for 5th year monthly salary= rs 400
  .
  .
  .
  .
  for 15th year monthly salary = 360+(12-1)40= rs 800
  his total salary for these 12 years = 12*12/2*(360*2+(12-1)*40)
  = rs 83520
  His monthly salary till retirement = rs 800
  let,no.of years he worked with this salary = x
  
  his average salary = (11520+83520+(800*12*x))/((3+12+x)*12)
  = 694(given)
  by solving this x= 23.49
  total service period = 23.49+12+3 =38.49>25
  so answer is a
• 10 years agoHelpfull: Yes(7) No(1)
• total salary for first 3 years where monthly salary is rs 320=320x12x3=11520
  total salary for 12 years with increment of 40=320+40=360x12x12=51840
  average given=694
  (51840-11520)/x=694
  x=40320/694=58 years
  answer=d
• 10 years agoHelpfull: Yes(3) No(3)
• salary he got in 3 yrs= 320*36=11520
  after increment of rs.40 per month, salary he got for 12 yrs= 360*144=51840
  avg salary he got till retirement= 694
  the no. of year he worked= (51840-11520)/694= 58 years
  
  so the ans is (d)
• 10 years agoHelpfull: Yes(2) No(3)
• SoIutlon The monthly salary for the first 3 years (i.e .. 36 months) = Rs 320
  . The monthly salary in the 4th year = Rs 360
  The monthly salary in .the 11thyear .. Ra 400
  The monthly salary in the 6th year = Ra 440
  The monthly salary in the Il1th year - [320 + 40(12») = Rs 800
  Now, as per the given problem,
  . .. [3(320) +!! [2(360) +(12 -1)40] + n(800)]_
  the average salary (3 + 12 + n) - Ra 698
  =
  ( 7920 + 800n) = 698
  15+n·
  n = 25
  :. The total service = (3 + 12 + 25) = 40 years.
  
  http://books.google.co.in/books?id=sO6mFHUuuVwC&pg=PA96&lpg=PA96&dq=the+monthly+salary+of+a+person+was+rs+320+for+each+of+the+first+three+years&source=bl&ots=jvYRhLwnuB&sig=Q8V_yu112Jkl90peZaxzOaO-tNI&hl=en&sa=X&ei=tuFUVJfnD8iQuQTyj4LwAQ&redir_esc=y#v=onepage&q=the%20monthly%20salary%20of%20a%20person%20was%20rs%20320%20for%20each%20of%20the%20first%20three%20years&f=false
  please ref page no 96
• 10 years agoHelpfull: Yes(1) No(1)