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`a) 5 / 13 xx 4 / 15 xx 13 = [ 5 xx 4 xx 13 ] / [ 13 xx 5 xx 3 ] = 4 / 3`
`b) ( 3 / 7 + 5 / 2 ) xx 7 / 5 = 3 / 7 xx 7 / 5 + 5 / 2 xx 7 / 5 = 3 / 5 + 7 / 2 = 6 / 10 + 35 / 10 = 41 / 10`
`c) 1 / 5 xx 11 / 18 + 11 / 18 xx 3 / 5 = 11 / 18 xx ( 1 / 5 + 3 / 5 ) = 11 / 18 xx 4 / 5 = [ 11 xx 2 xx 2 ] / [ 2 xx 9 xx 5 ] = 22 / 45`
\(a,\dfrac{5}{13}\times\dfrac{4}{15}\times13=\dfrac{4}{3}\)
\(b,\left(\dfrac{3}{7}+\dfrac{5}{2}\right)\times\dfrac{7}{5}=\left(\dfrac{6}{14}+\dfrac{35}{14}\right)\times\dfrac{7}{5}=\dfrac{41}{14}\times\dfrac{7}{15}=\dfrac{41}{30}\)
\(c,\dfrac{1}{5}\times\dfrac{11}{18}+\dfrac{11}{18}\times\dfrac{3}{5}=\dfrac{11}{18}\times\left(\dfrac{1}{5}+\dfrac{3}{5}\right)=\dfrac{11}{18}\times\dfrac{4}{5}=\dfrac{22}{45}\)
\(a,\dfrac{5}{13}\times\dfrac{4}{15}\times13=\dfrac{5\times4\times13}{13\times5\times3}=\dfrac{4}{3}\\ b,\left(\dfrac{3}{7}+\dfrac{5}{2}\right)\times\dfrac{7}{5}=\dfrac{3}{7}\times\dfrac{7}{5}+\dfrac{5}{2}\times\dfrac{7}{5}=\dfrac{3}{5}+\dfrac{7}{2}=\dfrac{6}{10}+\dfrac{35}{10}=\dfrac{41}{10}\\ c,\dfrac{1}{5}\times\dfrac{11}{18}+\dfrac{11}{18}\times\dfrac{3}{5}=\dfrac{11}{18}\times\left(\dfrac{1}{5}+\dfrac{3}{5}\right)=\dfrac{11}{18}\times\dfrac{4}{5}=\dfrac{22}{45}\)
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
a,17/23 + (1 - 17/23)
= 17/23 + 6/23
= 23/23 = 1
b,17/12 + 9/7 - (2/7 + 5 /12)
= (17/12 - 5/12) + (9/7 + 2/7)
= 1+1 = 2
c, 7/13 - ( 4/7 -6/13 )
= 7/13 - 4/7+ 6/13
= (7/13 + 6/13) -4/7
= 13/13 -4/7
= 1 -4/7 = 3/7
hok tốt✍️ ✍️
a) 17/23+(1-17/23)
=17/23+1-17/23
=1
b)17/12+9/7-(2/7+5/12)
=17/12+9/7-2/7-5/12
=1+1
=2
c)
7/13-(4/7-6/13)
=7/13-4/7+6/13
=1-4/7
=3/7
a) 17/23 + (1 - 17/23)
= 17/23 + 1 - 17/23
= (17/23 - 17/23) + 1
= 0 + 1 = 1
b) 17/12 + 9/7 - (2/7 + 5/12)
= 17/12 + 9/7 - 2/7 - 5/12
= (17/12 - 5/12) + (9/7 - 2/7)
= 1 + 1 = 2
c) 7/13 - (4/7 - 6/13)
= 7/13 - 4/7 + 6/13
= (6/13 + 6/12) - 4/7
= 1 - 4/7 = 3/7
d) 7/18 + 3/16 + 11/18 + 13/16
= (7/18 + 11/18) + (3/16 + 13/16)
= 1 + 1 = 1
d) sửa 7/18 + 3/16 + 11/18 + 13/16
= (7/18 + 11/18) + (3/16 + 13/16)
= 1 + 1
= 2
A) 3/7 + 4/9 + 4/7 + 5/9 = ( 4/9+5/9) + ( 3/7 + 4/7) = 1+ 1 = 2
B) 1/5 + 4/11 + 4/5 + 7/11 = ( 4/11 + 7/11) + ( 1/5 + 4/5) = 1+1=2
C) 1/15 + 4/15 + 5/18 + 7/18= ( 1/15+4/15) + (5/18+7/15)= 5/15 + 12/15 = 17/15
D) 1/8 + 1/12 + 3/8 + 5/12 = (1/8 + 3/8) + ( 1/12 + 1/12) = 4/8 + 2/12 = 64/96
K nha
\(a,\frac{15}{13}x\frac{4}{15}x13=\frac{15}{13}x13x.\frac{4}{15}=15x\frac{4}{15}=4\)
\(b,\left(\frac{3}{7}+\frac{5}{2}\right)x\frac{7}{5}=\frac{3}{7}x\frac{7}{5}+\frac{5}{2}x\frac{7}{5}=\frac{3}{5}+\frac{7}{2}=\frac{41}{10}\)
\(c,\frac{1}{5}x\frac{11}{18}+\frac{11}{18}x\frac{3}{5}=\frac{11}{18}\left(\frac{1}{5}+\frac{3}{5}\right)\)\(=\frac{11}{18}x\frac{4}{5}=\frac{22}{45}\)
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