Soldiers were practicing to shoot. Coincidence occurred, first soldier shoot the target in his first chance, second shoot the target in his 3rd
chance (i.e. 1 +2), third shoot in his 6th chance (i.e. 1+2+3), and so on. Total 9880 bullet were fired. Find the number of soldier.

• given
  1st soldier fired 1 bullet,
  2nd soldier fired 2 bullets,
  3rd soldier fired 6 bullets,
  ------
  so nth soldier fired {n*(n+1)/2} bullets.
  
  it forms a series like
  1+3+6+----+Tn
  Where Tn is the nth term of the series
  
  so Tn= {n*(n+1)/2}
  
  and sum= sigma[Tn]={n*(n+1)*(n+2)}/6
  
  given total bullets fired = 9880
  
  so, sum=9880
  
  {n*(n+1)*(n+2)}/6=9880
  
  solving this we get n= 38
  
  so, no. of soldiers =38.
• 10 years agoHelpfull: Yes(16) No(1)
• @Dipankar Dey,,,, In Elitmus question paper there are options.. so you have to do only check by opp for such type of questions.
• 10 years agoHelpfull: Yes(7) No(0)
• Ans=38
  
  1+3+6+10+15+21+28+36+...........= [N(N+1)(N+2) ] / 6
  
  PUT N=38
• 10 years agoHelpfull: Yes(4) No(2)
• how n(n+1)(n+2)/6
• 10 years agoHelpfull: Yes(3) No(0)
• Ans=38
  
  1+3+6+10+15+21+28+36+..........N (times) = [N(N+1)(N+2) ] / 6
  
  Where N is the no. of Soldiers
  
  PUT N=38
  (38x39x40)/6=9880.
  
• 10 years agoHelpfull: Yes(1) No(1)
• find the value of N by option which are given.
  
• 10 years agoHelpfull: Yes(1) No(0)
• bt my answer is 988.....for 3 soldier ....total...10....shoots....so for 9880 shoot.......988 soldier..
  
• 10 years agoHelpfull: Yes(1) No(3)
• how did u find the value of n in last line...
• 10 years agoHelpfull: Yes(0) No(0)
• 1+3+6+10+15+21+28+36+...........= [N(N+1)(N+2) ] / 6
  thus, n = 36...
• 10 years agoHelpfull: Yes(0) No(2)
• hhow can we get value of n?
• 10 years agoHelpfull: Yes(0) No(0)