=(10 + 20) + (11 + 19) + (12 + 18) + (13 + 17) + (14 + 16) +15
= 30 + 30 + 30 + 30 + 30 + 15
=165
10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20
= (10 + 20) + (11 + 19) + (12 + 18) + (13 + 17) + (14 + 16) + 15
= 30 + 30 + 30 + 30 + 30 + 15
= 30 x 5 + 15
= 150 + 15
= 165
k cho mk nha bn !
10 + 11 + 12 + 13 + 14 + 15 + 16 + 1 7 + 18 + 19 + 20
=(10 + 20) + (11 + 19) + (12 + 18) + (13 + 17) + (14 + 16) + 15
= 30 x 5 + 5
= 150 + 5
= 155
10 + 11 + 12 + 13 + 14 + 15 + 16 + 1 7 + 18 + 19 + 20
= ( 10 + 20 ) + ( 11 + 19 ) + ( 12 + 18 ) + ( 13 + 17 ) + ( 14 + 16 ) + 15
= 30 + 30 + 30 + 30 + 30 + 15
= 30 x 5 + 15
= 150 + 15
= 165
10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20
= ( 10 +20 ) + ( 11 + 19 ) + ( 12 + 18 ) + ( 13 + 17 ) + ( 14 + 16 ) + 15
= 30 + 30 + 30 + 30 + 30 + 15
= 30 x 5 + 15
= 150 + 15
= 165
10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20
= ( 10 + 20 ) + ( 11 + 19 ) +......+ ( 14 + 16 ) + 15
= 30 + 30 + 30 + 30 + 30 + 15
= 30 x 5 + 15
= 165
=> ( 10 + 20 ) x 5 + 15
=> 30 x 5 + 15
=> 150 + 15
=> 165
10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20
= (10+20)+(11+19)+(12+18)+(13+17)+(14+16)+15
=(30+30+30+30+30)+15
=30x5+15
=150+15
=165