Tính nhanh
a) 5,8 +( -3,75)+ 2,1 - (-1,25)
b) 4,7 +(-3,4)+5,19+3,4 +(-4,7)
c) 0,25 .1,58 . 4 - [ 1,25 .4,158 . (-8)]
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a) 17,56 . 4,7 + 5,3 . 17,56 - 2,8
= 17,56 . ( 4,7 + 5,3 ) - 2,8
= 17,56 . 10 - 2,8
= 175,6 - 2,8
= 172,8
b) ( 2 . 4 . 8 . 0,5 . 0,25 . 1,25 ) : 0,1
= [ ( 2 . 0,5 ) . ( 4 . 0,25 ) . ( 8 . 1,25 ) ] : 0,1
= ( 1 . 1 . 10 ) : 0,1
= 10 : 0,1
= 100
\(1,0,75-\dfrac{2}{3}-0,5=\dfrac{3}{4}-\dfrac{2}{3}-\dfrac{1}{2}=\dfrac{9}{12}-\dfrac{8}{12}-\dfrac{1}{2}=\dfrac{1}{12}-\dfrac{1}{2}\)
\(=\dfrac{2}{24}-\dfrac{12}{24}=\dfrac{-10}{24}=\dfrac{-5}{12}\)
\(2,\dfrac{1}{5}-0,125-\dfrac{5}{4}=\dfrac{1}{5}-\dfrac{1}{8}-\dfrac{5}{4}=\dfrac{8}{40}-\dfrac{5}{40}-\dfrac{5}{4}=\dfrac{3}{40}-\dfrac{5}{4}\)
\(=\dfrac{3}{40}-\dfrac{50}{40}=\dfrac{-47}{40}\)
\(3,1,25-\dfrac{3}{4}+\dfrac{4}{3}=\dfrac{5}{4}-\dfrac{3}{4}+\dfrac{4}{3}=\dfrac{2}{4}+\dfrac{4}{3}=\dfrac{6}{12}+\dfrac{16}{12}=\dfrac{22}{12}=\dfrac{11}{6}\)
\(4,0,15-\dfrac{1}{4}+\dfrac{2}{5}=\dfrac{3}{20}-\dfrac{1}{4}+\dfrac{2}{5}=\dfrac{3}{20}-\dfrac{5}{20}+\dfrac{2}{5}=\dfrac{-2}{20}+\dfrac{2}{5}\)
\(=\dfrac{-2}{20}+\dfrac{8}{20}=\dfrac{6}{20}=\dfrac{3}{10}\)
\(5,5-3,4+\dfrac{1}{5}=\dfrac{5}{1}-\dfrac{17}{5}+\dfrac{1}{5}=\dfrac{25}{5}-\dfrac{17}{5}+\dfrac{1}{5}=\dfrac{25-17+1}{5}=\dfrac{9}{5}\)
\(6,\dfrac{1}{4}-0,3+\dfrac{4}{3}=\dfrac{1}{4}-\dfrac{3}{10}+\dfrac{4}{3}=\dfrac{10}{40}-\dfrac{12}{40}+\dfrac{4}{3}=\dfrac{-2}{40}+\dfrac{4}{3}\)
\(=\dfrac{-1}{20}+\dfrac{4}{3}=\dfrac{-3}{60}+\dfrac{80}{60}=\dfrac{77}{60}\)
\(7,0,2-3,25+4,7=\dfrac{1}{5}-\dfrac{13}{4}+\dfrac{47}{10}=\dfrac{4}{20}-\dfrac{65}{20}+\dfrac{47}{10}=\dfrac{-61}{20}+\dfrac{47}{10}\)
\(=\dfrac{-61}{20}+\dfrac{94}{20}=\dfrac{33}{20}=1,65\)
\(8,5,4+\dfrac{-7}{3}-\dfrac{-5}{7}=\dfrac{27}{5}+\dfrac{-7}{3}-\dfrac{-5}{7}=\dfrac{81}{15}+\dfrac{-35}{15}-\dfrac{-5}{7}\)
\(=\dfrac{46}{15}-\dfrac{-5}{7}=\dfrac{322}{105}-\dfrac{-75}{105}=\dfrac{397}{105}\)
\(9,\dfrac{-4}{2}+\dfrac{1}{3}-\dfrac{1}{4}=\dfrac{-12}{6}+\dfrac{2}{6}-\dfrac{1}{4}=\dfrac{-10}{6}-\dfrac{1}{4}=\dfrac{-5}{3}-\dfrac{1}{4}\)
\(=\dfrac{-20}{12}-\dfrac{3}{12}=\text{ }\dfrac{-23}{12}\)
\(10,5,4-1,5-\left(7,2-1\right)=3,9-6,2=-2,3\)
\(11,4,9-\left(1,5-7,7+3\right)=4,9-\left(-3,2\right)=8,1\)
\(12,7,8-4,7+\left(5,3-1,4\right)=3,1+3,9=7\)
\(14,\dfrac{1}{2}-0,4+\dfrac{1}{5}\text{=}0,5-0,4+0,2=0,3\)
\(15,4,2-\dfrac{4}{5}+\dfrac{1}{2}=4,2-0,8+0,5=3,9\)
A=68,9+8,75+1,25
=68,9+(8,75+1,25)
=6,89+10=689
B=4,7 nhân 6,1+ 4,7 nhân 3,9
=4,7 nhân (6,1+3,9)
=4,7 nhân 10=47
\(a,2,3:0,25+7,7.4\\ =2,3.4+7,7.4\\ =\left(2,3+7,7\right).4=10.4=40\\ b,4,2.8+5,8:0,125\\ =4,2.8+5,8.8\\ =\left(4,2+5,8\right).8=10.8=80\\ c,3,4.4+5,6:0,25+4\\ =3,4.4+5,6.4+4\\ =\left(3,4+5,6+1\right).4=10.4=40\\ d,4:0,2+12:0,5+1,2:0,25\\ =4.5+12.2+1,2.4\\ 4.5+6.4+1,2.4\\ =4\left(5+6+1,2\right)\\ =4.12,2=48,8\)
a) 14,7 + (-8,4) + (-4,7) = (14,7 - 4,7) + (-8,4)
= 10 - 8,4 = 1,6
b) (-4,2).5,1 + 5,1.(-5,8) = 5,1. (- 4,2 - 5,8)
= 5,1. (-10) = -51
c) (-0,4: 0,04 + 10) . (1,2.20 + 12.8)
= (-10 + 10). (1,2.20 + 12.8)
= 0. (1,2.20 + 12.8) = 0.
b,4,7 + (-3,4) + 5,19 + 3,4 + (-4,7)
= [ 4,7 + (-4,7)] + [(-3,4) + 3,4] + 5,19
= 0 + 0 + 5,19
= 5,19