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a) \(\dfrac{2}{5}-\dfrac{3}{15}\)
\(=\dfrac{2}{5}-\dfrac{3:3}{15:3}\)
\(=\dfrac{2}{5}-\dfrac{1}{5}\)
\(=\dfrac{1}{5}\)
b) \(\dfrac{9}{27}-\dfrac{2}{9}\)
\(=\dfrac{9:3}{27:3}-\dfrac{2}{9}\)
\(=\dfrac{3}{9}-\dfrac{2}{9}\)
\(=\dfrac{1}{9}\)
c) \(\dfrac{18}{24}-\dfrac{4}{8}\)
\(=\dfrac{18:6}{24:6}-\dfrac{4:2}{8:2}\)
\(=\dfrac{3}{4}-\dfrac{2}{4}\)
\(=\dfrac{1}{4}\)
d) \(\dfrac{6}{16}-\dfrac{10}{64}\)
\(=\dfrac{6\times2}{16\times2}-\dfrac{10:2}{64:2}\)
\(=\dfrac{12}{32}-\dfrac{5}{32}\)
\(=\dfrac{7}{32}\)
`# \text {DNamNgV}`
`16/21 + 6/7`
`= 16/21 + 18/21`
`= 34/21`
__
`15/22 \times 11/35`
`= (15 \times 11)/(22 \times 35)`
`= (5 \times 3 \times 11)/(2 \times 11 \times 5 \times 7)`
`= (3 \times 1)/(2 \times 7)`
`= 3/14`
___
`8/11 \div 5/22`
`= 8/11 \times 22/5`
`= (8 \times 22)/(11 \times 5)`
`= (8 \times 11 \times 2)/(11 \times 5)`
`= (8 \times 2)/5`
`= 16/5`
___
`9/13 \div 27/39`
`= 9/13 \times 39/27`
`= 9/13 \times 13/9`
`= 1`
a/\(\left(\dfrac{7}{9}\times\dfrac{9}{7}\right)\times\dfrac{25}{28}\)
\(=1\times\dfrac{25}{28}\)
\(=\dfrac{25}{28}\)
b/\(\dfrac{4}{7}\times\dfrac{17}{18}\times\dfrac{7}{4}\times\dfrac{18}{17}\)
\(=\left(\dfrac{4}{7}\times\dfrac{7}{4}\right)\times\left(\dfrac{17}{18}\times\dfrac{18}{17}\right)\)
\(=1\times1\)
\(=1\)
\(\dfrac{1}{2}-\dfrac{3}{8}=\dfrac{4}{2\times4}-\dfrac{3}{8}=\dfrac{4}{8}-\dfrac{3}{8}=\dfrac{1}{8}\)
\(\dfrac{4}{3}-\dfrac{8}{15}=\dfrac{4\times5}{3\times5}-\dfrac{8}{15}=\dfrac{20}{15}-\dfrac{8}{15}=\dfrac{12}{15}=\dfrac{4}{5}\)
\(\dfrac{5}{6}-\dfrac{7}{12}=\dfrac{5\times2}{6\times2}-\dfrac{7}{12}=\dfrac{10}{12}-\dfrac{7}{12}=\dfrac{3}{12}=\dfrac{1}{4}\)
\(\dfrac{11}{4}-\dfrac{9}{8}=\dfrac{11\times2}{4\times2}-\dfrac{9}{8}=\dfrac{22}{8}-\dfrac{9}{8}=\dfrac{13}{8}\)
\(\dfrac{17}{16}-\dfrac{3}{4}=\dfrac{17}{16}-\dfrac{3\times4}{4\times4}=\dfrac{17}{16}-\dfrac{12}{16}=\dfrac{5}{16}\)
\(\dfrac{31}{36}-\dfrac{5}{6}=\dfrac{31}{36}-\dfrac{5\times6}{6\times6}=\dfrac{31}{36}-\dfrac{30}{36}=\dfrac{1}{36}\)
a) 4/9 x ( 3/5 + 8/5 - 2/10 )
= 4/9 x 1
=4/9
b) ( 312 + 325 - 247 ) : 13
= 390 : 13
= 30
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