100 Followers!

Algebra Level 1

Find the last digit of 1+2+3+4+....100.


The answer is 0.

Fred Fan by fred fan , 21, Canada

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

Mohammad Khaza
Aug 4, 2017

1 + 2 + 3 + . . . . . . . . . . . + 100 = 100 × 101 2 = 5050 1+2+3+...........+100=\frac{100 \times 101}{2}=5050

so, the last digit is 0

1 Helpful 0 Interesting 0 Brilliant 0 Confused

actually, it should be 100 × 101 2 \dfrac{100\times 101}{2}

Bloons Qoth - 3 years, 5 months ago

Log in to reply

thank you very much.that was typing mistake.

Mohammad Khaza - 3 years, 5 months ago
Alex Li
Jun 2, 2015

1 + 2 + 3 + . . . + 100 = ( 100 ) ( 101 ) 2 = 5050 ≡ 0 m o d 10 1+2+3+...+100=\frac{(100)(101)}{2}=5050 \equiv \boxed{0} \mod10 .

1 Helpful 0 Interesting 0 Brilliant 0 Confused

Did the same way!

Swapnil Das - 6 years ago
Matin Naseri
Feb 22, 2018

( n ) ( n + 1 ) 2 \frac{(n)(n+1)}{2}

( 100 ) ( 100 + 1 ) 2 \frac{(100)(100+1)}{2} = 5050

505 \text{505} 0 \boxed{0}

0 Helpful 0 Interesting 0 Brilliant 0 Confused

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...