A nice sum

Algebra Level 1

n = 1 8 n 2 = ? \large\sum_{n=1}^8 n^2 = \ ?

204 5463 12 9

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18 solutions

Nihar Mahajan
Dec 19, 2014

sum of squares from 1 to n = n * (n+1) * (2n+1) / 6

here n =8

by substituting n = 8 we get 8 * (8+1 ) * (16+1) / 6

= 8 * 9 * 17 / 6

= 204 :)

well,there are only 8 no.s & greatest number is 8 2 = 64 , 8^{2} =64, so the answer won't be greater than 5000 , we know answer is not 9 or 12. So only logical choice is 204

Jithin Saseendran - 6 years, 5 months ago

How to derive this formula ?

Yahya Salah - 6 years, 5 months ago

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try telescopic sum with (x+1)^3 - x^3

Nihar Mahajan - 6 years, 5 months ago
Rostam Dana
Dec 19, 2014

Everybody will think it first (y)

Shohag Farazi - 6 years, 5 months ago

=1^2+2^2+3^2+4^2+5^2+6^2+7^2+8^2 =1+4+9+16+25+36+49+64=204 AND FORMULA Sum= [N(N+1)(2N+1)]/6 N=8 =(8x9x17)/6=4x3x17=204

You are great , dear Sir!

Irfan Ullah - 6 years, 5 months ago
Saiful Islam
Dec 21, 2014

n(n+1)(2n+1)/6 where n=8

Dipu Islam
Dec 25, 2014

Here, Lower limit of n=1 and Upper limit of n=8 Then,

Anna Anant
Dec 24, 2014

1^2+2^2+3^2+4^2+5^2+6^2+7^2+8^2 204

Md Moniruzzaman
Jan 8, 2015

sum of squares from 1 to n = n * (n+1) * (2n+1) / 6 here n =8 by substituting n = 8 we get 8 * (8+1 ) * (16+1) / 6 = 8 * 9 * 17 / 6 = 204

n(n+1)(2n+1)/6, sum of squares up to n.

Plugging in 8, we get

8(9)(17)/6=204.

Saiful Robin
Jan 1, 2015

Its better way to use the formula. That is -

1^2 + 2^2 + 3^2 + . . . . . . + n^2 = {n * (n+1) * (2n+1)}/6 ; Where n=8

Ayaz Jaskani
Dec 30, 2014

Took square of each digit from 1 to 8 and added them up.

Ans : 204 sum of squares of 1 to 8 is the answer

Tejas Sharma
Dec 30, 2014

that's so easy SUM= n * (n+1) * (2n+1) / 6.

Narendra Rao
Dec 30, 2014

In this question have three question mark ,and options are given in single,two,three,and four digit numbers ,here 204 is only three digit number so i choose that correct one taht's it.

Kevin Bowie
Dec 29, 2014

Well My simple logic by seeing multiple choices is 8x8=64 So it's impossible for 12 and 9 Then if 8x8=64, below of 8 (7x7, 6x6), they won't be more than 64 100x8 = 800 < 5463 So it's really impossible too 204 must be true hehe

1+4+9+16+25+36+49+64=204

(1×1)+(2×2)+(3×3)+(4×4)+(5×5)+(6×6)+(7×7)+(8×8) =1+4+9+16+25+36+49+64=204

I did the same as Jithin, wihout any formula, 8² = 64, so... if 64 > 12 & 9, this options were dropped, and only I have 2 options, 5463 & 204, so the ans is 204

Helen Caintic
Dec 27, 2014

1x1+2x2+3x3+4x4+5x5+6x6+7x7+8x8=? ; then
1+4+9+16+25+36+49+64= 204

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