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3 x 15 + 21 x 15 + 85 x 5
= 45 + 315 + 425
= 785
15 - 30 + 40
= 25
21 + 19 - 50 + 10
= 0
\(\dfrac{1}{5}-\dfrac{1}{4}+2\)
\(=-\dfrac{1}{20}+2\)
\(=\dfrac{39}{20}\)
\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)
\(=\dfrac{5}{12}\times\dfrac{1}{4}\)
\(=\dfrac{5}{12}\times\dfrac{3}{12}\)
\(=\dfrac{5}{48}\)
\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)
\(=-\dfrac{9}{20}\)
\(3\times15+21\times15+85\times5\\ =15\times\left(3+21\right)+425\\ =15\times24+425\\ =360+425\\ =785\)
\(15-30+40\\ =\left(15+40\right)-30\\ =55-30\\ =25\)
\(21+19-50+10\\ =\left(21+19\right)-\left(50-10\right)\\ =40-40\\ =0\)
\(\dfrac{1}{5}-\dfrac{1}{4}+2\)
\(=\dfrac{4}{20}-\dfrac{5}{20}+\dfrac{40}{20}\)
\(=\dfrac{\left(4+40\right)}{20}-\dfrac{5}{20}\)
\(=\dfrac{44}{20}-\dfrac{5}{20}\)
\(=\dfrac{39}{20}\)
\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)
\(=\dfrac{5}{12}\times\dfrac{1}{4}\)
\(=\dfrac{5}{48}\)
\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)
\(=\dfrac{2}{20}+\dfrac{4}{20}-\dfrac{15}{20}\)
\(=\dfrac{6}{20}-\dfrac{15}{20}\)
\(=-\dfrac{9}{20}\)
( 5 + 5 + 5 + 5 ) : 4 - ( 10 + 10 - 15 ) : 2
= 20 : 4 - 5 : 2
= 5 - 2,5
= 2,5
Đáp số : 2,5
\(\left(\frac{9}{10}+\frac{1}{10}\div\frac{4}{5}\right)\times\left(\frac{3}{15}-\frac{2}{15}\times\frac{4}{3}\times\frac{9}{8}\right)\)
\(=\left(1\div\frac{4}{5}\right)\times\left(\frac{3}{15}-\frac{1}{5}\right)\)
\(=\frac{5}{4}\times0\)
\(=0\)
a (1/6 + 1/10 + 1/15) : (1/6 + 1/10 - 1/15)
= ( 5/30 + 3/30 + 2/30) : (5/30 + 3/30 - 2/30)
= 1/3 : 1/6 = 1/3 x 6/1 = 6/3 = 2
b (1/2 - 1/3 + 1/4 - 1/5) : (1/4 - 1/5)
= (1/2 - 1/3 + 1/4 - 1/5) : (1/4 - 1/5)
= 1/2 - 1/3 = 1/6
`4/7 + 2/3 = 12/21 + 14/21 = 26/21`
`5/6 -3/4 = 10/12 - 9/12 = 1/12`
`3/10 xx 15/6 = 3/10 xx 5/2 = 3/4`
`7/6 : 5/4 = 7/6 xx 4/5 = 14/15`
4/15 + 5/10
= 8/30 + 15/30
= 23/30
23/30