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a) \(1678\cdot24+77\cdot1678-1678=1678\left(24+77-1\right)=167800\)
b) Ta có: \(\dfrac{2}{5}+\dfrac{4}{11}+\dfrac{3}{5}+\dfrac{18}{11}+\dfrac{1}{4}+\dfrac{1}{6}\)
\(=\left(\dfrac{2}{5}+\dfrac{3}{5}\right)+\left(\dfrac{4}{11}+\dfrac{18}{11}\right)+\dfrac{1}{4}+\dfrac{1}{6}\)
\(=3+\dfrac{1}{4}+\dfrac{1}{6}\)
\(=\dfrac{36}{12}+\dfrac{3}{12}+\dfrac{2}{12}=\dfrac{41}{12}\)
Bài 5:
a: =1/3+2/5
=5/15+6/15
=11/15
b: =6/21+12/21=18/21=6/7
c: =16/24+10/24
=26/24
=13/12
d: =4/12+3/12+10/12
=17/12
e: =19/24-9/24
=10/24
=5/12
f: =8/9-3/9=5/9
g: =9/3+1/3=10/3
k: =15/24+42/24+14/24
=71/24
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+10
=20+20+20+20+20+20+20+20+20+10
=20*9+10
=180+10=190
1+2+3+4+5+6+7+8+9+10+11+12+13 +14 +15+16+17+18+19
= 19 - 1( tức là trừ đi số 10 vì nó tròn chục )
= 18 : 2
= 9 x ( 19 + 1 ) + 10
= 9 x 20 + 10
= 180 + 10
= 190
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+20+10
=20+20+20+20+20+20+20+20+20+20+10
=20×10+10
=200+10
=210
= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) + (4 + 16 ) + ( 5 + 15 ) + ( 6 + 14 ) + ( 7 + 13 ) + ( 8 + 12) + ( 9+ 11 ) + 20
= 20 + 20 + 20 +20 + 20 +20 + 20 + 20 + 20 +20
= 20 x 10
= 200
tui đầu tiên đó
1: =72/90+65/90=137/90
2: =24/56-77/56=-53/56
3: =-7/10+4/5=1/10
4: =15/100-4/100=11/100
5: =4/6-5/6=-1/6
6: =10/40-15/40-76/40=-81/40
7: =-9/10+7/18
=-81/90+35/90=-46/90=-23/45
8: =27/90-55/90=-28/90=-14/45
9: =36/60-50/60-35/60=-49/60
10: =-4/9+5/6-3/8
=-32/72+60/72-27/72
=1/72
\(\frac{3}{5}\times\frac{6}{7}+\frac{3}{5}:7+\frac{6}{5}\)
\(=\frac{3}{5}\times\frac{6}{7}+\frac{3}{5}\times\frac{1}{7}+\frac{6}{5}\)
\(=\frac{3}{5}\times\left(\frac{6}{7}+\frac{1}{7}\right)+\frac{6}{5}\)
\(=\frac{3}{5}\times1+\frac{6}{5}\)
\(=\frac{3}{5}+\frac{6}{5}=\frac{9}{5}\)
~ Hok tốt ~
\(\frac{29}{12}:\frac{1}{2}-\frac{5}{12}:\frac{1}{2}-\frac{1}{2}\)
\(=\left(\frac{29}{12}-\frac{5}{12}\right):\frac{1}{2}-\frac{1}{2}\)
\(=2:\frac{1}{2}-\frac{1}{2}\)
\(=4-\frac{1}{2}=\frac{7}{2}\)
~ Hok tốt ~
(19+1)+(18+2)+(17+3)+(16+4)+(15+5)+(14+6)+(13+7)+(12+8)+(11+9)+20)+10
=20+20+20+20+20+20+20+20+20+20=(20*10)+10
=210
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+(10+20)
=20+20+20+20+20+20+20+20+20+30
=(20 x 9) + 30
=180 + 30
=210
tk nha
\(\dfrac{4}{3}+\dfrac{7}{6}+\dfrac{2}{3}+\dfrac{5}{6}\)
\(=\left(\dfrac{4}{3}+\dfrac{2}{3}\right)+\left(\dfrac{7}{6}+\dfrac{5}{6}\right)\)
\(=\dfrac{6}{3}+\dfrac{12}{6}\)
\(=2+2=4\)
\(\dfrac{18}{11}:\dfrac{12}{11}-\dfrac{1}{8}+\dfrac{5}{2}\)
\(=\dfrac{6\cdot3\cdot11}{11\cdot6\cdot2}-\dfrac{1}{8}+\dfrac{20}{8}\)
\(=\dfrac{3}{2}-\dfrac{1}{8}+\dfrac{20}{8}\)
\(=\dfrac{12}{8}-\dfrac{1}{8}+\dfrac{20}{8}=\dfrac{31}{8}\)
\(\dfrac{4}{5}\cdot\dfrac{3}{7}+\dfrac{4}{5}\cdot\dfrac{6}{7}-\dfrac{4}{5}\cdot\dfrac{4}{14}\)
\(=\dfrac{4}{5}\left(\dfrac{3}{7}+\dfrac{6}{7}-\dfrac{2}{7}\right)\)
\(=\dfrac{4}{5}\cdot1=\dfrac{4}{5}\)
\(\dfrac{5}{3}:\dfrac{3}{4}\cdot\dfrac{4}{5}\)
\(=\dfrac{5}{3}\cdot\dfrac{4}{3}\cdot\dfrac{4}{5}=\dfrac{5\cdot4\cdot4}{3\cdot3\cdot5}\)
\(=\dfrac{16}{9}\)
`4/3 + 7/6 + 2/3 + 5/6`
`= (4/3 +2/3 )+(7/6 +5/6)`
`= 6/3+ 12/6`
`= 2+2`
`=4`
__
`18/11 : 12/11 -1/8 +5/2`
`=18/11 xx 11/12 - 1/8 +5/2`
`= 18/12 -1/8+5/2`
`= 3/2 -1/8+5/2`
`=(3/2 +5/2)-1/8`
`=4-1/8`
`=31/8`
__
`4/5 * 3/7 + 4/5 * 6/7 - 4/5 * 4/14`
`= 4/5*(3/7 + 6/7 - 4/14)`
`= 4/5*1`
`=4/5`
__
`5/3 : 3/4 * 4/5`
`= 5/3 * 4/3 * 4/5`
`= 20/9 * 4/5`
`=80/45`
`=16/9`
`#` Chúc cậu năm mới vui vẻ.