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Câu a:
\(x\) x 30 = 210
\(x\) = 210 : 30
\(x\) = 7
Câu b:
\(x\) x 15 + \(x\) x 5 = 2800
\(x\) x (15 + 5) = 2800
\(x\) x 20 = 2800
\(x\) = 2800 : 20
\(x\) = 140
Câu c:
(\(x\) + 15) x 50 = 13700
\(x\) + 15 = 13700 : 50
\(x\) + 15 = 274
\(x\) = 274 - 15
\(x\) = 259
X × 3 + x × 7 = 6600
X x (3 + 7) = 6600
X x 10 = 6600
X = 6600 : 10
X = 660
a)\(\dfrac{5}{7}+\dfrac{4}{9}=\dfrac{45}{63}+\dfrac{28}{63}=\dfrac{73}{63}\) ; \(\dfrac{9}{11}+\dfrac{3}{8}=\dfrac{72}{88}+\dfrac{33}{88}=\dfrac{105}{88}\)
\(\dfrac{4}{5}-\dfrac{2}{3}=\dfrac{12}{15}-\dfrac{10}{15}=\dfrac{2}{15}\); \(\dfrac{16}{25}-\dfrac{2}{5}=\dfrac{16}{25}-\dfrac{10}{25}=\dfrac{6}{25}\)
b)\(5+\dfrac{3}{5}=\dfrac{25}{5}+\dfrac{3}{5}=\dfrac{28}{5};10-\dfrac{9}{16}=\dfrac{160}{16}-\dfrac{9}{16}=\dfrac{151}{16}\)
\(\dfrac{2}{3}-\left(\dfrac{1}{6}+\dfrac{1}{8}\right)=\dfrac{2}{3}-\left(\dfrac{8}{48}+\dfrac{6}{48}\right)=\dfrac{2}{3}-\dfrac{14}{48}=\dfrac{32}{48}-\dfrac{14}{48}=\dfrac{3}{8}\)
3/5=21/35, 5/7=25/35
suy ra : 3/5+x/35=5/7 = 21/35 + x/35 =25/35
x/35 =25/35 - 21/35
x/35 =4/35
x =4
nho k cho minhf vi minh nhanh nhat
\(a.\dfrac{3\times4\times7}{12\times8\times9}=\dfrac{3\times4\times7}{3\times4\times4\times2\times9}\\ =\dfrac{7}{4\times2\times9}=\dfrac{7}{72}\\ b.\dfrac{4\times5\times6}{12\times10\times8}=\dfrac{4\times5\times2\times3}{4\times3\times5\times2\times4\times2}=\dfrac{1}{8}\\ c.\dfrac{5\times6\times7}{12\times14\times15}=\dfrac{5\times6\times7}{2\times6\times7\times2\times5\times3}\\ =\dfrac{1}{2\times2\times3}=\dfrac{1}{12}\)
\(TL:\)
x × 3 + x × 7 = 6600
X x (3 + 7) = 6600
X x 10 = 6600
X = 6600 : 10
X= 660
HT and t i c k
P/s : Đúng nha
\(\frac{15}{17}\times\frac{51}{5}< x< \frac{67}{9}+\frac{35}{9}\)
\(\Rightarrow9< x< \frac{102}{9}\)
\(\Rightarrow9< x< 12\)
\(\Rightarrow x=10\)hoặc \(x=11\)
Vậy \(x=10\)hoặc \(x=11\)
a: \(\dfrac{35}{8}\times2\times\dfrac{5}{17}+\dfrac{35}{8}\times\dfrac{5}{17}+\dfrac{35}{8}\times\dfrac{2}{17}\)
\(=\dfrac{35}{8}\left(\dfrac{10}{17}+\dfrac{5}{17}+\dfrac{2}{17}\right)\)
\(=\dfrac{35}{8}\times\dfrac{17}{17}=\dfrac{35}{8}\)
b: \(\dfrac{6}{7}\times\dfrac{6}{27}+\dfrac{33}{77}\times\dfrac{15}{27}-\dfrac{3}{7}\)
\(=\dfrac{3}{7}\times\dfrac{12}{27}+\dfrac{3}{7}\times\dfrac{15}{27}-\dfrac{3}{7}\)
\(=\dfrac{3}{7}\left(\dfrac{12}{27}+\dfrac{15}{27}-1\right)=\dfrac{3}{7}\times0=0\)