The sum

1 - 2 + 3 - 4 + ... + 53 - 54 + 55


is

• ans :28
  1-2+3-4+....+53-54+55
  1-2=-1 ,3-4=-1... ,53-54=-1(27 pairs)
  -27+55=28
  
• 11 years agoHelpfull: Yes(23) No(0)
• Ans : 28
  The sum of the first 2 digits is -1
  There are 54 terms,therefore sum is -27
  55-27=28
  
• 11 years agoHelpfull: Yes(3) No(0)
• ans=28
  1+3+....55=28*28
  2+4+.....54=28*27
  28*28-27*27
  28(28-27)
  28
• 11 years agoHelpfull: Yes(2) No(0)
• (28*28)-(28*27)=28
  even numbers 27
  odd numbers 28
  calculating sum of n numbers in a.p= n/2(2a+(n-1)*d)
  
• 11 years agoHelpfull: Yes(1) No(0)
• 28 ans
  -27+55=28
• 11 years agoHelpfull: Yes(1) No(0)
• (1+3+5+...............+55)-(2+4+...............54)
  =>28
• 11 years agoHelpfull: Yes(0) No(0)
• 55-27=28 will be the answer
  
• 11 years agoHelpfull: Yes(0) No(0)