Question

Tính Nhanh 

a 10+12+14+16+18+20

b 1+3+5+7+9+11+13+15+17+19

c 75+110+25+90+200

Answer 1

a ) 10 + 12 + 14 + 16 + 18 + 20 

= ( 10 + 20 ) + ( 14 + 16 ) + ( 12 + 18 )
=  30 + 30 + 30 

=  90

b ) 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19

= ( 19 + 1 ) + ( 17 + 3 ) + ( 15 + 5 ) + ( 7 + 13 ) + ( 9 + 11 )

= 20 + 20 + 20 + 20 + 20

= 100

c ) 75 + 110 + 25 + 90 + 200

= ( 75 + 25 ) + ( 110 + 90 ) + 200

= 100 + 200 + 200

= 500

do em chưa học tính chất dãy số nên không còn cách nhanh hơn 

Answer 2

a 10 + 12 + 14 + 16 + 18 + 20

= ( 10 + 20 ) + ( 14 + 16 ) + ( 12 + 18 )

= 40 + 40 + 40

= 40 x 3

= 120

b 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19

= ( 1 + 19 ) + ( 3 + 17 ) + ( 5 + 15 ) + ( 7 + 13 ) + ( 9 + 11 )

= 20 + 20 + 20 + 20 + 20

= 20 x 5

= 100

c 75 + 110 + 25 + 90 + 200

= ( 75 + 25 ) + ( 110 + 90 ) + 200

= 100 + 200 + 200

= 500

Answer 3

10+12+14+16+18+20=90

1+3+5+7+9+11+13+15+17+19=100

75+110+25+90+200=500

tk nhé

Answer 4

a) 10+12+14+16+18+20

= (10+20)+(12+18)+(14+16)

=      30    +     30   +       30

=    90

b)1+3+5+7+9+11+13+15+17+19

=(1+19)+(3+17)+(5+15)+(7+13)+(9+11)

=    20   +   20    +    20  +    20   +    20

=      100

c)75+110+25+90+200

=(75+25)+(110+90)+200

=     100  +      200  +200

=    500

Answer 5

a 10+12+14+16+18+20

=(10+20)+(12+18)+(14+16)

=30+30+30

=90

b 1+3+5+7+9+11+13+15+17+19

=(1+19)+(3+17)+(5+15)+...+(9+11)(5 cặp)

=20+20+20+20+20

=100

c 75+110+25+90+200

=(75+25)+(110+90)+200

=100+200+200

=500

Answer 6

a)10+12+14+16+18+120

=(10+20)+(12+18)+(14+16)

=30+30+30

=90

b)1+3+5+7+9+11+13+15+17+19

=(1+19)+(3+17)+(5+15)+(7+13)+(9+11)

=20+20+20+20+20

=100

c)75+110+25+90+200

=(75+25)+(110+90)+200

=100+200+200

=500

đúng 100%

Answer 7

a 10+12+14+16+18+20

= ( 10 + 20 ) + ( 12 + 18 ) + ( 14 + 16 )

= 30 + 30 + 30

= 30 x 3

= 90

b) b 1+3+5+7+9+11+13+15+17+19

= ( 1 + 19 ) + ( 3 + 17 ) + ( 5 + 15 ) + ( 7 + 13 ) + ( 9 + 11 ) 

= 20 + 20 + 20 + 20 + 20

= 20 x 5

= 100

c 75+110+25+90+200

= ( 75 + 25 ) + ( 110 + 90 ) + 200

= 100 + 200 + 200

= 100 + 100 + 100 + 100 + 100

= 100 x 5

= 500 

Answer 8

a) = ( 10 + 20 ) + ( 12 + 18 ) + ( 14 + 16 )

   =    30          +      30       +      30

   =                30 x 3

  =                    90

b) = ( 1 + 19 ) +  ( 3 + 17 ) + ( 5 +  15 ) + ( 7 + 13 ) + ( 9 + 11 )

   =      20      +       20      +      20       +      20      +      20

  =                                     20 x 5

  =                                       100

c) = ( 75 + 25 ) + ( 110 + 90 ) + 200

   =       100      +      200       +      200

   =             100 + ( 200 x 2 )

   =             100 +    400

  =                   500