**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 ??

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

Sum of first n odd numbers = n²

ReplyDeletesum of first n odd numbers = n^2

ReplyDeleten*n is the solution

ReplyDelete50 * 50 = 2500 (sum of first 50 odd numbers).

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

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

DeleteHA! GAAAAAAAAAAAAAAAAAAAAAAAAY

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

DeleteU just use a calculator? It doesn't say u can't use it

Deleteyeah u do u just added up to the number 49 not 99 which would equal 2500

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

ReplyDeletejust use the formula

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

a=first term (1)

n=number of terms (75)

d=common difference(2)

and???

Deleteand you will get answer

Deletei think that this is for people that enjoy solving puzzles and are not impatient like me!

ReplyDeletethis question is bekar

ReplyDeletethis is very simple promblem.

ReplyDeletejust think !

The answer is 5625.

ReplyDelete50*50=2500

ReplyDeleteit's that sum of first x odd numbers=x*x or x^2

so,75*75=5625 is the answer

1+99=100

ReplyDelete3+97=100

5+95=100...

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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...

.

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middle term be 75+75=150

75/2=37.5

so ans = (150*37.5)=5625

lol......

DeleteThis comment has been removed by the author.

ReplyDelete75*75=5625

ReplyDeleteFor the first 50 odd numbers you would go up to 99 not 50 ;)

ReplyDeletethe formula is n/2(2*a + (n-1) d) n=50 ,a=1 ,d=2

ReplyDelete