lấy (19 + 11) + (12 + 18) + (13 + 17) + (14 + 16) +15 = 135
11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19
= ( 11 + 19 ) + ( 12 + 18 ) + ( 13 + 17 ) + ( 14 + 16 ) + 15
= 20 + 20 + 20 + 20 + 15
= 20 x 4 + 15
= 80 + 15
= 95
11+19+12+13+14+15+16+17+18+19
=(11+19)+(12+18)+(13+17)+(16+14)+15
=20+20+20+20+15
=20x4+15
=80+15
=95
11+12+13+14+15+16+17+18+19=
(11+19)+(12+18)+(13+17)(14+16)+15=
20+20+20+20+15=
80+15=95
11+12+13+14+15+16+17+18+19
=(11+19)+(12+18)+(13+17)+(14+16)+15
= 30 + 30 + 30 + 30 + 15
= 120+15
= 135