A group of 630 children is arranged in a row for a group photograph session. Each row contains three fewer children than the row in front of it. What number of rows is not possible?
A. 3
B. 4
C. 5
D. 6
E. 7

• solve through options
  we know s = n/2 [2a+(n-1)d)
  here common difference is -3
  put n=4
  here sum s = 630
  so, 630=4/2[2a+(4-1)(-3)]
  630=4a-18
  4a=648
  a= 648/4=162
  so arrangement be 162+159+156+153=630
  so number of rows is 4
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• 9 years agoHelpfull: Yes(2) No(1)
• Number of row=6 is not possible
  Sum of arithmetic series whose difference is d is given as ;S=n/2*(2a+(n-1)*d)
  a=(2s/n-(n-1)*d)/2
  d=3 and S=630 are constant;
  if n=3; a=207; Hence, 207+210+213=630. Similarily;
  n=4; a=153; Hence. 153+156+159+162=630.
  ..............
  n=6; a=195/2 NOT POSSIBLE
• 9 years agoHelpfull: Yes(2) No(1)