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b, 3/5 + 4/7 + 2/8 + 10/25 + 9/21 + 28/16
= 3/5 + 4/7 + 2/8 + 2/5 + 3/7 + 14/8
= (3/5 + 2/5) + ( 4/7 + 3/7) + ( 2/8 + 14/8)
= 1 + 1 + 7/4
= 2 + 7/4 = 15/4
c , 8/7 + 7/6 + 5/8 + 10/12 + 24/28 + 6/16
= c , 8/7 + 7/6 + 5/8 + 5/6 + 6/7 + 1/2
= (8/7 + 6/7) + (7/6 + 5/6) + 5/8 + 1/2
= 14/7 + 12/6 + 5/8 + 1/2
= 2 + 2 + 5/8 + 1/2
= 4 + 9/8 = 41/8
Bài 1:
\(\dfrac{2}{3}\) + \(\dfrac{3}{4}\) - \(\dfrac{2}{5}\)
=\(\dfrac{40}{60}\) + \(\dfrac{45}{60}\) - \(\dfrac{24}{60}\)
= \(\dfrac{61}{60}\)
b; \(\dfrac{12}{13}\) x \(\dfrac{3}{4}\) - \(\dfrac{7}{13}\)
= \(\dfrac{9}{13}\) - \(\dfrac{7}{13}\)
= \(\dfrac{2}{13}\)
c; \(\dfrac{15}{17}\) : \(\dfrac{19}{34}\) - \(\dfrac{17}{19}\)
= \(\dfrac{15}{17}\) x \(\dfrac{34}{19}\) - \(\dfrac{17}{19}\)
= \(\dfrac{30}{19}\) - \(\dfrac{17}{19}\)
= \(\dfrac{13}{19}\)
Bài 2:
a; \(\dfrac{x}{5}\) x \(\dfrac{3}{7}\) = \(\dfrac{9}{35}\)
\(\dfrac{x}{5}\) = \(\dfrac{9}{35}\) : \(\dfrac{3}{7}\)
\(\dfrac{x}{5}\) = \(\dfrac{3}{5}\)
\(x\) = \(\dfrac{3}{5}\) x 5
\(x\) = 3
1.
\(\frac{5}{3}-\frac{1}{4}+\frac{1}{3}-\frac{3}{4}\)
\(=\left(\frac{5}{3}+\frac{1}{3}\right)-\left(\frac{1}{4}+\frac{3}{4}\right)\)
\(=2-1=1\)
\(\frac{2}{7}\cdot\frac{1}{5}+\frac{2}{7}\cdot\frac{4}{5}=\frac{2}{7}\cdot\left(\frac{1}{5}+\frac{4}{5}\right)=\frac{2}{7}\cdot1=\frac{2}{7}\)
#Louis
\(1.a)\frac{5}{3}-\frac{1}{4}+\frac{1}{3}-\frac{3}{4}\)
\(=\left(\frac{5}{3}+\frac{1}{3}\right)-\left(\frac{1}{4}+\frac{3}{4}\right)\)
\(=2-1\)
\(=1\)
\(b)\frac{2}{7}\times\frac{1}{5}+\frac{2}{7}\times\frac{4}{5}\)
\(=\frac{2}{7}\times\left(\frac{1}{5}+\frac{4}{5}\right)\)
\(=\frac{2}{7}\times1\)
\(=\frac{2}{7}\)
\(2.a)\frac{5}{6}+\frac{7}{12}-\frac{2}{9}\)
\(=\frac{30}{36}+\frac{21}{36}-\frac{8}{36}\)
\(=\frac{43}{36}\)
\(b)\frac{4}{9}\times\frac{5}{8}+\frac{1}{6}\)
\(=\frac{5}{18}+\frac{1}{6}=\frac{5}{18}+\frac{3}{18}\)
\(=\frac{8}{18}=\frac{4}{9}\)
\(c)2:\frac{3}{11}-\frac{13}{12}\)
\(=2\times\frac{11}{3}-\frac{13}{12}\)
\(=\frac{22}{3}-\frac{13}{12}\)
\(=\frac{25}{4}\)
A, X x 3/5 + X x 7/5 = 9/4 B, X - 4/7 = 1/5 : 7/2
<=> X x (3/5 + 7/5) = 9/4 <=> X - 4/7 = 2/35
<=> X x 2 = 9/4 <=> X = 2/35 + 4/7 <=> X = 22/35
<=> X= 9/4 : 2 <=> X = 9/8
#HT#
\(a,x.\frac{3}{5}+x.\frac{7}{5}=\frac{9}{4}\)
\(\Leftrightarrow x.\left(\frac{3}{5}+\frac{7}{5}\right)=\frac{9}{4}\)
\(\Leftrightarrow x.2=\frac{9}{4}\)
\(\Leftrightarrow x=\frac{9}{8}\)
\(b,x-\frac{4}{7}=\frac{1}{5}:\frac{7}{2}\)
\(\Leftrightarrow x-\frac{4}{7}=\frac{2}{35}\)
\(\Leftrightarrow x=\frac{22}{35}\)
1.
a. = 135 x ( 6 + 4 )
= 135 x 10
= 1350
b. = 432 x (4 + 3 + 2 + 1)
= 432 x 10
= 4320
2.
a. X x (2 + 3 + 4) = 234
X x 9 = 234
X = 234 : 9
X = 26
b. X x (1 + 2) = 12
X x 3 = 12
X = 12 : 3
X = 4
c. X x (1 + 3 + 5) = 135
X x 9 = 135
X = 135 : 9
X = 15
A)135x(4+6)=135x10=1350
B)432x(4+3+2+1)=432x10=4320
A)Xx(2+3+4)=234
Xx9=234
X=36
1) 1/2*1/6=1/12 ; 1/3*1/4=1/12. Ta có : 17/5+1/12*71/5-1/12*28/5=1/12*(17/5+71/5-28/5)=1/12*60/5=1/12*12=1 2)1/10+4/20+9/30+16/40+25/50 =1/10+2/10+3/10+4/10+5/10(rút gọn) =15/10=3/2 3)18/15*(2525/3636+1515/1818-2020/7272)=6/5*(25/36+5/6-5/18)(rút gọn)=6/5*25/36+6/5*5/6-6/5*5/18=5/6+1-1/3=9/6=3/2.
Tính bằng 2 cách :
a). 234 x 25 + 234 x 75
C1: \(234\times25+234\times75\)
\(=5850+17550\)
\(=23400\)
C2: \(234\times25+234\times75\)
\(=234\times\left(25+75\right)\)
\(=234\times100\)
\(=23400\)
b). 765 x 123 - 755 x 23
C1: \(765\times123-765\times23\)
\(=94095-17595\)
\(=76500\)
C2: \(765\times123-765\times23\)
\(=765\times\left(123-23\right)\)
\(=765\times100\)
\(=76500\)
=> Bạn xem lại đề ạ!
c). 476 x ( 45 + 55 )
C1: \(476\times\left(45+55\right)\)
\(=476\times100\)
\(=47600\)
C2: \(476\times\left(45+55\right)\)
\(=476\times45+476\times55\)
\(=21420+26180\)
\(=47600\)
d). 2415 : 5 : 5
=> Xem lại đề ạ
e). ( 76 x 28 ) : 7
C1: \(\left(76\times28\right)\div7\)
\(=2128\div7\)
\(=304\)
C2: \(\left(76\times28\right)\div7\)
\(=76\times\left(28\div7\right)\)
\(=76\times4\)
\(=304\)
g). ( 175 + 29070 ) : 5
C1: \(\left(175+29070\right)\div5\)
\(=29245\div5\)
\(=5849\)
C2: \(\left(175+29070\right)\div5\)
\(=175\div5+29070\div5\)
\(=35+5814\)
\(=5849\)
h). ( 3224 - 1236 ) : 4
C1: \(\left(3224-1236\right)\div4\)
\(=1988\div4\)
\(=497\)
C2: \(\left(3224-1236\right)\div4\)
\(=3224\div4-1236\div4\)
\(=806-309\)
\(=497\)