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[ ( 4x + 28 ) + 55 ] : 25 = 7
( 4x + 28 ) + 55 = 7 x 25
( 4x + 28 ) + 55 = 175
4x + 28 = 175 - 55
4x + 28 = 120
4x = 120 - 28
4x = 92
x = 92 : 4
x = 23
[ ( 4x + 28 ) . 3 + 55 ] : 25 = 7
( 4x + 28 ) . 3 + 55 = 7 x 25
( 4x + 28 ) . 3 + 55 = 175
( 4x + 28 ) . 3 = 175 - 55
( 4x + 28 ) . 3 = 120
4x + 28 = 120 : 3
4x + 28 = 40
4x = 40 - 28
4x = 12
x = 12 : 4
x = 3
3/25 x ( 15/7 - 2/7 ) + 3/7 x 1/25
= 3/25 x 13/7 + 3/7 x 1/25
= (3 x 13/7 + 3/7 ) x 1/25
= 42/7 x 1/25
= 6 x 1/25
= 6/25
\(\dfrac{3}{25}\times\dfrac{15}{7}+\dfrac{3}{7}\times\dfrac{1}{25}-\dfrac{2}{7}\times\dfrac{3}{25}\)
\(=\dfrac{3}{25}\times\left(\dfrac{15}{7}-\dfrac{2}{7}\right)+\dfrac{3}{7}\times\dfrac{1}{25}\)
\(=\dfrac{3}{25}\times\dfrac{13}{7}+\dfrac{3}{7}\times\dfrac{1}{25}\)
\(=\dfrac{3\times13}{25\times7}+\dfrac{3\times1}{7\times25}\)
\(=\dfrac{39}{175}+\dfrac{3}{175}\)
\(=\dfrac{39+3}{175}\)
\(=\dfrac{42}{175}\)
\(=\dfrac{6}{25}\)
\(a,MSC:195\\ \dfrac{7}{15}=\dfrac{7.13}{15.13}=\dfrac{91}{195}\\ \dfrac{5}{13}=\dfrac{5.15}{13.15}=\dfrac{75}{195}\\ b,MSC:48\\ \dfrac{11}{12}=\dfrac{11.4}{12.4}=\dfrac{44}{48}\)
Giữ nguyên \(\dfrac{7}{48}\)
\(c,MSC:30\\ \dfrac{3}{2}=\dfrac{3.15}{2.15}=\dfrac{45}{30}\\ \dfrac{2}{3}=\dfrac{2.10}{3.10}=\dfrac{20}{30}\\ \dfrac{7}{5}=\dfrac{7.6}{5.6}=\dfrac{42}{30}\\ d,MSC:75\\ \dfrac{5}{3}=\dfrac{25.5}{3.25}=\dfrac{125}{75}\\ \dfrac{15}{25}=\dfrac{15.3}{25.3}=\dfrac{45}{75}\)
\(\dfrac{7}{15}=\dfrac{7.13}{15.13}=\dfrac{91}{195};\dfrac{5}{13}=\dfrac{5.15}{13.15}=\dfrac{75}{195}\)
\(\dfrac{11}{12}=\dfrac{11.4}{12.4}=\dfrac{44}{48}\) ; giữ nguyên phân số còn lại
\(\dfrac{3}{2}=\dfrac{3.15}{2.15}=\dfrac{45}{30};\dfrac{2}{3}=\dfrac{2.10}{3.10}=\dfrac{20}{30};\dfrac{7}{5}=\dfrac{7.6}{5.6}=\dfrac{42}{30}\)
\(\dfrac{5}{3}=\dfrac{5.25}{3.25}=\dfrac{125}{75};\dfrac{15}{25}=\dfrac{15.3}{25.3}=\dfrac{45}{75}\)
5 x 7 x 77 - 7 x 60 + 49 x 25 -15 x 42
= 5x7x77 - 7x5x12 + 7x7x5x5 - 5x3x7x6
= 35 x77 - 35x12 + 35x35 - 35x18
= 35 x ( 77-12+35-18 )
= 35 x 82 = 2870
\(\dfrac{24}{35}:\dfrac{15}{7}=\dfrac{24}{35}\times\dfrac{7}{15}=\dfrac{8}{25}\)
\(\Rightarrow chọn\) \(B\)
`# \text {DNamNgV}`
\(\dfrac{24}{35} \div \dfrac{15}{7} \\ = \dfrac{24}{35} \times \dfrac{7}{15} \\ = \dfrac{8}{25}\)
Chọn đáp án B.
(4.x+25):15=7
(4.x+25)=7.15
(4.x+25)=105
4.x=105-25
4.x=80
x=80:4
x=20
x=20