5:Tính nhanh
a) -37+54+(-70)+(-163)+246 b) -359+181+(-123)+350+(-172)
c) -69+53+46+(-94)+(-14)+78 d) 13-12+11+10-9+8-7-6+5-4+3+2-1
Đáp án + Giải thích các bước giải:
Ta có :
`a)-37+54+(-70)+(-163)+246`
`=-(37+163)+(246+54)-70`
`=-200+300-70`
`=100-70`
`=30`
`b)-359+181+(-123)+350+(-172)`
`=-350-9+172+9-123+350-172`
`=-350+172-123+350-172`
`=(172-172)+(350-350)-123`
`=0+0-123`
`=-123`
`c)-69+53+46+(-94)+(-14)+78`
`=-78+9+(53+46)-94-14+78`
`=(78-78)+(-94-14+9)+(53+46)`
`=0+(-99)+99`
`=0`
`d)13-12+11+10-9+8-7-6+5-4+3+2-1`
`=(13-12)+(10-9)+(8-7)+(5-4)+(2-1)+(11-6+3)`
`=1+1+1+1+1+8`
`=13`
a)-37+54+(-70)+(-163)+246
= ( 246 + 54 ) – ( 163 + 37 ) – 70
= 300 – 200 – 70
=100 -70
= 30
b) -359+181+(-123)+350+(-172)
=( 350 – 359 + 181 ) – 172 -123
= 172 – 172 -123
=-123
c) -69+53+46+(-94)+(-14)+78
= ( -69 + 53 -14 ) + ( 78 + 46 – 94 )
= -30 + 30
=0
d) 13-12+11+10-9+8-7-6+5-4+3+2-1
= ( 13 – 12 ) + ( 10 – 9 ) + (8 – 7) + ( 5 – 4 ) + ( 2 – 1 ) + ( 11 – 6 + 3)
= 1 + 1 + 1 + 1 +1 + 8
=13