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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 ??

1. Sum of first n odd numbers = n²

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

3. n*n is the solution

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

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

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

2. HA! GAAAAAAAAAAAAAAAAAAAAAAAAY

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

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

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

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

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)

1. and you will get answer

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

7. this question is bekar

8. this is very simple promblem.
just think !

10. 50*50=2500
it's that sum of first x odd numbers=x*x or x^2

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

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

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