Number Trick Riddle

Number Trick Riddle - 16 june

Sonal asked the class to see if they could find the sum of the first 50 odd numbers. As everyone settled down to their addition, Lavesh ran to her and said, 'The sum is 2,500.' Ms. Sonal thought, 'Lucky guess,' and gave him the task of finding the sum of the first 75 odd numbers. Within 20 seconds, Lavesh was back with the correct answer

How does Lavesh find the sum so quickly and what is the answer ??


For Solution: Click Here

22 comments:

  1. Sum of first n odd numbers = n²

    ReplyDelete
  2. sum of first n odd numbers = n^2

    ReplyDelete
  3. n*n is the solution

    50 * 50 = 2500 (sum of first 50 odd numbers).

    75 * 75 = 5625 (sum of first 75 odd numbers).

    ReplyDelete
    Replies
    1. yes but if you add 1+3+5+7...etc you don't get anywhere near 2500. same for up to 75

      Delete
    2. HA! GAAAAAAAAAAAAAAAAAAAAAAAAY

      Delete
    3. it's first 75 odd numbers not, upto 75. so the sum is 1+3+5+....+149

      Delete
    4. U just use a calculator? It doesn't say u can't use it

      Delete
    5. yeah u do u just added up to the number 49 not 99 which would equal 2500

      Delete
  4. you just hv to square the numbers, n for that you dont hv to boast yourself so much in that puzzle of urs

    ReplyDelete
  5. just use the formula

    s=n/2[2a+(n-1)d]

    a=first term (1)
    n=number of terms (75)
    d=common difference(2)

    ReplyDelete
  6. i think that this is for people that enjoy solving puzzles and are not impatient like me!

    ReplyDelete
  7. this question is bekar

    ReplyDelete
  8. this is very simple promblem.
    just think !

    ReplyDelete
  9. The answer is 5625.

    ReplyDelete
  10. 50*50=2500
    it's that sum of first x odd numbers=x*x or x^2
    so,75*75=5625 is the answer

    ReplyDelete
  11. 1+99=100
    3+97=100
    5+95=100...
    .
    .
    25th time 49+51=100
    because 1st is 1 , 2nd is 3=(2*2-1),3rd is 5(3*2-1)
    .... 25th be 49 (25*2-1);

    similarly for
    75
    1+149=150;
    3+147=150...
    .
    .
    .
    middle term be 75+75=150
    75/2=37.5
    so ans = (150*37.5)=5625

    ReplyDelete
  12. This comment has been removed by the author.

    ReplyDelete
  13. For the first 50 odd numbers you would go up to 99 not 50 ;)

    ReplyDelete