An intelligent boy is doing a jigsaw with 275 pieces. Each day that he fits pieces together there are fewer pieces left, and it is reasonable to assume that he fits more pieces each day because the number left to sort out diminishes progressively. Hence he is able to fit an extra piece as each day goes by. On the first day he fits 20 pieces. How many days does it take for him to complete the puzzle?

a) 11 b) 10 c) 12 d) 13

• . pieces fitted pieces left
  1st day 20 255
  2nd day 21 234
  3rd day 22 212
  ...
  10th day 29 30
  11th day 30 -
  Hence, at 11th day, he would had completed the task.
• 11 years agoHelpfull: Yes(1) No(0)
• we know that sum of n number= n/2[2a+(n-1)d]
  where a=20,d=1;
  n/2[2*20+(n-1)1]=275
  n[n+39]=550
  n^2+39n-550=0
  n^2+50n-11n-550=0
  (n-11)(n-50)=0
  n-11=0;
  n=11(Days)--------(A)
• 9 years agoHelpfull: Yes(0) No(1)