11+22+33+44+55+66+77+88+99
= ( 11 + 88 ) + ( 22 + 77 ) + ( 33 + 66 ) + ( 44 + 55 ) + 99
= 99 + 99 + 99 + 99 + 99
= 99 x 5
= 495
10+20+30+40+50
= ( 10 + 40 ) + ( 20 + 30 ) + 50
= 50 + 50 + 50
= 50 x 3
= 150
K mình nha mình nhanh nhất đó!
ai k mik mik ks lại
11+22+33+44+55+66+77+88+99
=(11+99)+(22+88)+(33+77)+(44+66)+55
=110+110+110+110+55
=110*4+55
=440+55
=495
10+20+30+40+50
=(10+50)+(20+40)+30
=60+60+30
=60*2+30
=120+30
=150
(11+99)+(22+88)+(33+77)+(44+66)+55=
100+100+100+100+55=
= 455
(10+40)+(30+20)+50=
50+50+50=150
(11+99)+(22+88)+(77+33)+(66+44)+55=100+100+100+100+55=455
(10+50)+(20+30)+40=60+60+40=180
tính nhanh :
11 + 22 + 33 + 44 + 55 + 66 + 77 + 88 + 99
=(11 + 99) + (22 + 88) + (33 + 77) + (44 + 66) + 55
= 110 + 110 + 110 + 110 + 55
= 110 x 4 + 55
= 495
10 + 20 + 30 + 40 + 50
= (10 + 40) + (20 + 30) + 50
= 50 + 50 + 50
= 50 x 3
= 150
k mình tch lại
11+22+33+44+55+66+77+88+99+10+20+30+40+50=645