Problem that needs hardwork?

Algebra Level 3

n = 1 1 0 11 n 2 + n = 1 1 0 8 n 3 = ? \large \sum_{n=1}^{10^{11}} n^2 +{\sum_{n=1}^{10^{8}}} n^3 = ?


The answer is 358333333838333335833350000000000.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Rushikesh Jogdand
Mar 12, 2016

The Problem Student got answer by observation.

Hard workers find solution by the formula i = 1 n i 2 = n ( n + 1 ) ( 2 n + 1 ) 6 \large \sum_{i=1}^{n} i^2 = \frac{n(n+1)(2n+1)}{6} and i = 1 n i 3 = ( n ( n + 1 ) 2 ) 2 \sum_{i=1}^{n} i^3 = {(\frac{n(n+1)}{2})}^{2}

But calculators would float.

What irony!

Yes, it is an irony. :P

Ashish Menon - 5 years, 3 months ago
Ashish Menon
Mar 5, 2016

Answer of equation 1 is 333333333338333333333350000000000 333333333338333333333350000000000
Answer of equation 2 is 25000000500000002500000000000000 25000000500000002500000000000000
So, their sum is 358333333838333335833350000000000 358333333838333335833350000000000


For equation 1

First i found n = 1 10 n 2 \large \sum_{n=1}^{10} n^2 = 385

n = 1 100 n 2 \large \sum_{n=1}^{100} n^2 = 338350

n = 1 1000 n 2 \large \sum_{n=1}^{1000} n^2 = 333833500

n = 1 10000 n 2 \large \sum_{n=1}^{10000} n^2 = 333383335000

So, we observe thar in each case one additional 3 is being added to the left and right of 8. Similarly, one additional 0 is being added to the right of 0. When i am finding for 100 there are two 3s on left of 8 and one 3 on right of 8 and one 0 on right of 5. So, for 100000000000, there should be eleven 3s on the left of 8, ten 3s on right of 8 and ten 0s on right of 5.i.e 333333333338333333333350000000000 333333333338333333333350000000000 .


For equation 2

First i found n = 1 100 n 3 \sum_{n=1}^{100} n^3 = 25502500

n = 1 1000 n 3 \sum_{n=1}^{1000} n^3 = 250500250000

n = 1 10000 n 3 \sum_{n=1}^{10000} n^3 = 2500500025000000

So, we find that in every case an additional 0 is being added to the left and right of the second 5 in each case. Then to the right of the third 5, twice the number of 0s as the njmber of them to the right of the second 5 is present. For, 1000, there is one 0 to the left of the second 5 and two 0s to the right of it. Then there are 2×2 zeroes to right of the third 5 of the number. So, for 100000000, there would be six zeroes to the left of the second 5, seven 0s to the right of them and to the right of the third 5, there would be 7×2=14 zeroes. i.e. 25000000500000002500000000000000 25000000500000002500000000000000


So, the final answer is 333333333338333333333350000000000 333333333338333333333350000000000 + 25000000500000002500000000000000 25000000500000002500000000000000 = 358333333838333335833350000000000 358333333838333335833350000000000

You calculated them manually ?

Akshat Sharda - 5 years, 3 months ago

Log in to reply

Yes, i found a trick, so i did it manually. I have edited my solution showing you the way i did it

Ashish Menon - 5 years, 3 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...