Question

Tính bằng cách thuận tiện nhất 10-11+12-13+14-15+16-17+18-19+20

Answer 1

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
= 15

Answer 2

(20 + 10) - (11 + 19) + ( 12 + 18 ) - ( 13 + 17 ) + ( 14 + 16 ) - 15

= 30 - 30 + 30 - 30 - 15

= -15

Answer 3

(20+10)-(11+19)+(12+18)-(13+17)+(14+16)-15

=30-30+30-30-15+30

=15

Answer 4

10-11+12-13+14-15+16-17+18-19+20

=(10+20)-(11+19)-(12+18)-(13+17)-(14+16)-15

=15

Answer 5

=30-30+30-30+30-15

=15

Answer 6

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
= 15