Numbers numbers

What is the ten's digit of 1 1 22 11^{22} ?

5 8 1 2 4

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.

3 solutions

1 1 22 = ( 10 + 1 ) 22 = 1 0 22 + . . . + ( 22 21 ) 10 ˙ 1 21 + 1 22 = 1 0 22 + . . . + 22 ˙ 10 ˙ 1 + 1 22 = . . . 221 \begin{aligned} 11^{22} & = (10+1)^{22} \\ & = 10^{22} +...+\begin{pmatrix} 22 \\ 21 \end{pmatrix} 10 \dot{} 1^{21} + 1^{22} \\ & = 10^{22} +...+22\dot{}10\dot{}1 + 1^{22} \\ & = ...221 \end{aligned}

The ten's digit is therefore 2 \boxed{2} .

Same approach!!

Aakash Khandelwal - 5 years, 3 months ago
Jase Jason
Mar 20, 2016

11^2 = 121 11^3 = 12321 11^4 = 1234321 etc. Notice how every time, the tens in always 2.

Nikola Djuric
Mar 5, 2016

11²²=121¹¹=21¹¹=21x441^5=21x41^5= 21x41*1681²=861x81²=61x6561=61²= 3721=21 (mod 100) so our digit is 2 Also 11ⁿ gives reminders 11,21,31,41,51,61,71,81,91,01 when divided by 100 and repeating every 10th,so 22=2(mod 10) so 11²²=21(mod 100) so 2 is answer

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...