1+2+3.............+100=幾多

1+2+3.............+100
=100(1+100)/2=5050

1+2+3...........+100=5050

0+100= 100
1+99 = 100
2+98=100
3+97=100
..................
49+51=100

以上有50次即 50 x 100 = 5000
再加中間的50
答案便是 5000+50
5050

口訣:頭項+尾項x項數除2

=1+100x100
----------------
2

10100
=---------
2

=5050
====

(1+100)x(100/2)
=101x50
=5050

(1 + n)n/2
=(1 + 100)100/2
=5050

1+2+3........+100=5050
因為1+2=3,3+3=6.........=100=5050

5020,because 1+10=45 11+20..............................

1+2+3.............+100=
100(1+100)/2
=5050

(1+100)*100/2
=101*100/2
=101*50
=5050
係5050

{(1+100)x100}/2 = 5050