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a) 86 - 39 - 21 = 47 - 21
= 26
b) 115 - 57 - 15 = ( 115 - 15 ) - 57
= 100 - 57
= 43
c) 4 + 8 + 12 + 16 + 20 + 24 + 28 = ( 4 + 8 + 16 + 20 + 24 + 28 ) + 12
= 100 + 12
= 112
a) 86-39-21 = 86-(39+21) = 86-60 = 26
b) 115-57-15 = 115-15-57 = 100-57 = 43
c) (4+28)+(8+24)+(12+20)+16 = 32+32+32+16 = 32 x 3 + 16 = 112
a: =3990-(463*72-39^2):15
=3990-2121=1869
b: =1995-963-172=860
c: =33/11-7/11=26/11
d: =3/2+5=13/2
`@` `\text {Answer}`
`\downarrow`
`a,`
`3990 - (463 \times 72 - 39 \times 39) \div 15`
`= 3990 - (33336 - 1521) \div 15`
`= 3990 - 31815 \div 15`
`= 3990 - 2121`
`= 1869`
`b,`
`1995 - 321 \times 3 - 6020 \div 35`
`= 1995 - 963 - 172`
`= 1032 - 172`
`= 860`
`c,`
`3 - 7/11`
`= 33/11 - 7/11`
`= 26/11`
`d,`
`1/4 \div 1/6 + 5`
`= 1/4 \times 6 + 5`
`= 3/2 + 5`
`= 13/2`
câu 1.1/4 ngày, 2/3 ngày, 1/3 ngày, 72 giờ
câu 2. chiều dài thật là
200 x 2 = 400 (cm) => 4(m)
\(\dfrac{3}{4}\times\dfrac{5}{7}=\dfrac{15}{28};\dfrac{5}{8}\times\dfrac{4}{15}=\dfrac{20}{120}=\dfrac{1}{6};\dfrac{7}{12}\times\dfrac{4}{9}=\dfrac{28}{108}=\dfrac{7}{27};\)
\(\dfrac{1}{6}\times\dfrac{3}{5}=\dfrac{3}{30}=\dfrac{1}{10};\dfrac{12}{21}\times\dfrac{23}{8}=\dfrac{276}{168}=\dfrac{23}{14};\dfrac{13}{4}\times\dfrac{5}{39}=\dfrac{65}{156}=\dfrac{5}{12}\)
\(\dfrac{7}{42}\times\dfrac{13}{21}=\dfrac{91}{882}=\dfrac{13}{126};\dfrac{3}{16}\times\dfrac{4}{15}=\dfrac{12}{240}=\dfrac{1}{20}\)
`4/7+4`
`=4/7+4/1`
`=4/7+28/7`
`=32/7`
__
`3+6/11`
`=33/11+6/11`
`=39/11`
__
`3-5/7`
`=3/1-5/7`
`=21/7-5/7`
`=16/7`
__
`21/9-2`
`=21/9-18/9`
`=3/9`
`=1/3`
__
`15/24+2`
`=15/24+48/24`
`=63/24`
`=21/16`
__
`63/45-20/25`
`=63/45-4/5`
`=63/45-36/45`
`=27/45`
`=9/15`
__
`3/4-2/8`
`=3/4-1/4`
`=2/4`
__
`6/7-5/8`
`=48/56-35/56`
`=13/56`
__
`37/45-5/9`
`=37/45-25/45`
`=12/45`
`=4/15`
__
`46/39-11/13`
`=46/39-33/39`
`=13/39`
`=1/2`
__
`5/12+3/4+1/3`
`=5/12+9/12+4/12`
`=14/12+4/12`
`=18/12`
`=3/2`
__
`1/2+3/7+11/14`
`=7/14+6/14+11/14`
`=13/14+11/14`
`=24/14`
`=12/7`
__
`7/10-(1/5+1/4)`
`=7/10-(4/20+5/20)`
`=7/10-9/20`
`=14/20-9/20`
`=5/20`
`=1/4`
__
`15/4-2/3-3/4`
`=(15/4-3/4)-2/3`
`=12/4-2/3`
`=3-2/3`
`=9/3-2/3`
`=7/3`
a - 420 : ( x : 39 ) = 105
⇒ x : 39 = 420 : 105
⇒ x : 39 = 4
⇒ x = 4 * 39
⇒ x = 156
a) -420 :(x:39)=105
x:39=-420 : 105
x : 39=\(\dfrac{-14}{5}\)
x=\(\dfrac{-546}{5}\)
73 882 919 > 39 113 031
22 222 22 < 1 000 000 000
2 500 300 = 2 000 000 + 500 000 + 300
4 300 000 > 3 000 000 + 400 000
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