A light was seen at intervals of 13 seconds. It was seen for the first time at 1 hr 54 min 50 secs. a. m. and the last time at 3 hrs 17 min 49 secs. a.m. How many times was light seen ?

a. 378
b. 375
c. 360
d. 384

• It is an A.P.
  where a=1hr 54min 50sec= 6890 sec.
  (last term) L=3hr 17min 49sec= 11869sec.
  d=13.
  L=a+(n-1)d
  11869=6890+(n-1)13.
  4979=(n-1)13
  n-1=383.
  n=384
  hence number of times light was seen is 384
  
• 9 years agoHelpfull: Yes(4) No(0)
• Interval=13s
  60/13=4.61538462(seen in 1 min)
  time interval=1:54:50 to 3:17:49=83min
  83*4.61538462=384
• 9 years agoHelpfull: Yes(2) No(1)