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1)
a) 21/23 x 5/11 x 4/35
= \(\frac{21.5.4}{23.11.35}\)
= \(\frac{7.3.5.4}{23.11.5.7}\)
= \(\frac{3.4}{23.11}\) ( ta đã rút gọc 7 và 5 )
= \(\frac{12}{253}\)
b) 26 x 13/42 : 13
= \(\frac{26.13}{42.13}\)
= \(\frac{13.2.13}{21.2.13}\)
= \(\frac{13}{21}\)
c) 5/9 : 2/9 + 4/9 : 2/3
= \(\frac{5.9}{9.2}+\frac{4.3}{9.2}\)
= \(\frac{5}{2}+\frac{2.2.3}{3.3.2}\)
= \(\frac{5}{2}+\frac{2}{3}\)
= \(\frac{19}{6}\)
2 ) tìm x
a ) 2 - x = 1/3 + 1/6
2 - x = 1/2
x = 2 - 1/2
x = 3/2
b ) x + 5/8 = 1 + 3/4
x + 5/8 = 7/4
x = 7/4 - 5/8
x = 9/8
3)
a) x < 3/4 + 4/5
=> x < 31/20
=> x = 1
b) 1/2 + 3/5 < x < 5/4
=> 11/10 < x < 5/4
ta quy đồng phân số 11/10 và 5/4
\(\frac{11}{10}=\frac{11.4}{10.4}=\frac{44}{40}\)
\(\frac{5}{4}=\frac{5.10}{4.10}=\frac{50}{40}\)
=> 44/40 < x < 50/40
=> x không thỏa mãn
a) \(\frac{2}{3}+\frac{3}{4}+\frac{4}{5}+\frac{1}{3}+\frac{1}{4}+\frac{1}{5}\)
= \(\left(\frac{2}{3}+\frac{1}{3}\right)+\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{4}{5}+\frac{1}{5}\right)\)
= \(\frac{3}{3}+\frac{4}{4}+\frac{5}{5}\)
= \(1+1+1\)
= \(3\)
b) \(\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{4}{6}+\frac{9}{12}+\frac{16}{20}\)
= \(\left(\frac{1}{3}+\frac{4}{6}\right)+\left(\frac{1}{4}+\frac{9}{12}\right)+\left(\frac{1}{5}+\frac{16}{20}\right)\)
= \(\left(\frac{1}{3}+\frac{2}{3}\right)+\left(\frac{1}{4}+\frac{3}{4}\right)+\left(\frac{1}{5}+\frac{4}{5}\right)\)
= \(\frac{3}{3}+\frac{4}{4}+\frac{5}{5}\)
= \(1+1+1\)
= \(3\)
ko sai được... đúng 100%
a)2/3+3/4+4/5+1/3+1/4+1/5
= ( 2/3 + 1/3 ) + ( 3/4 + 1/4 ) + ( 4/5 + 1/5 )
= 1 + 1 + 1 = 3
b) 1/3 + 1/4 + 1/5 + 4/6 + 9/12 + 16/20
= 1/3 + 1/4 + 1/5 + 2/3 + 3/4 4/5
= ( 1/3 + 2/3 ) + ( 1/4 + 3/4 ) + ( 1/5 + 4/5 )
= 1 + 1 + 1 = 3
\(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}=\frac{1}{2}+\left(-\frac{1}{3}+\frac{1}{3}\right)+\left(-\frac{1}{4}+\frac{1}{4}\right)-\frac{1}{5}=\frac{1}{2}-\frac{1}{5}=\frac{3}{10}\)
= 1/2 - 1/5 = 2/5 (giải thích chút nha -1/3+ 1/3 = 0 ; -1/4 + 1/4 = 0 và sau khi quy đồng ta được kq như tớ đã tính)
\(3.5.36+15.42+30.11\)
\(=15.36+15.42+15.\left(2.11\right)\)
\(=15.36+15.42+15.22\)
\(=15.\left(36+42+22\right)\)
\(=15.100=1500\)
3x5x36+15x42+30x11
=15x36+15x42+15x2x11
=15x36+15x42+15x22
=15x(36+42+22)
=15x100
=1500
hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
\(\frac{5}{6}-\left(\frac{2}{5}+\frac{1}{3}\right)\)
\(=\frac{5}{6}-\frac{11}{15}\)
\(=\frac{1}{10}\)
tíc mình nha
\(\frac{5}{6}-\left(\frac{2}{5}+\frac{1}{3}\right)=\frac{5}{6}-\frac{11}{15}=\frac{1}{10}\)
Ta có :
16 - 2 x 8 = 16 - 16 = 0
Số nào nhân với 0 cũng bằng 0
Dãy trên = 0
\(a,\frac{2}{3}.\frac{4}{5}+\frac{1}{3}.\frac{2}{5}\)
= \(\frac{2}{5}.\frac{4}{3}+\frac{1}{3}.\frac{2}{5}=\frac{2}{5}\left(\frac{4}{3}+\frac{1}{3}\right)=\frac{2}{5}.\frac{5}{3}=\frac{2}{3}\)
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