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120 x 64 + 320 - 25 x 4 x 16 = 120 x 4 x 16 + 20 x 16 - 100 x 16
= 480 x 16 + 20 x 16 - 100 x 16
= 16 x (480 + 20 - 100)
= 16 x 400
= 6400
\(\frac{4}{3}.\frac{9}{8}.\frac{16}{15}.\frac{25}{24}...\frac{121}{120}.\frac{144}{143}\)
\(=\frac{2.2}{1.3}.\frac{3.3}{2.4}.\frac{4.4}{3.5}.\frac{5.5}{4.6}...\frac{11.11}{10.12}.\frac{12.12}{11.13}\)
\(=\frac{2.2.3.3.4.4.5.5...11.11.12.12}{1.3.2.4.3.5.4.6...10.12.11.13}\)
\(=\frac{\left(2.3.4.5...11.12\right).\left(2.3.4.5...11.12\right)}{\left(1.2.3.4...10.11\right).\left(3.4.5.6...12.13\right)}\)
\(=\frac{12.2}{1.13}\)
\(=\frac{24}{13}\)
( Dấu \(.\)là dấu \(\times\)nha )
1) 25 + 91 + 75 + 101
= (25+75) + (91 + 101)
= 100 + 192
= 292
2) 41 x 39 - 41 x 9
= 41 x (39 - 9)
= 41 x 30
= 1230
3) 710 x 99 + 710
= 710 x 99 + 710 x 1
= 710 x (99 + 1)
= 710 x 100
= 71000
4) 17 x 85 + 15 x 17 - 120
= 17 x (85 + 15) - 120
= 17 x 100 -120
= 1700 -120
= 1580
5) (39 x 42 - 37 x 42) : 42
= 42 x (39 - 37) : 42
= 42 x 2 : 42
= 84 : 42
=2
6) 120 - 48 - 52
= 120 - (48 + 52)
= 120 - 100
= 20
7) 23 x 75 + 25 x 23 + 180
= 23 x (75 + 25) +180
= 23 x (75 + 25) +180
= 23 x 100 + 180
= 2300 +180
=2480
8) 2448 : [119 - (23 - 6)]
= 2448 : (119 - 17)
= 2448 : 102
= 24
a) = 9/5 + 3/4 + 1/4 + 6/5
= ( 9/5 + 6/5 ) + ( 3/4 + 1/4 )
= 3 + 1
= 4
\(\frac{\left(120+60\right)}{12}=\frac{120}{12}+\frac{60}{12}=10+5=15\)
\(78\cdot31+78\cdot17+78\cdot24+22\cdot72=78\left(31+17+24\right)+22\cdot72\)
\(=78\cdot72+22\cdot72=72\left(78+22\right)=72\cdot100=7200\)
\(997+86=997+\left(83+3\right)=\left(997+3\right)+83\)
\(=1000+83=1083\)
\(5\cdot25\cdot2\cdot37\cdot4=\left(5\cdot2\right)\cdot\left(25\cdot4\right)\cdot37\)
\(=10\cdot100\cdot37=37000\)
\(558+336+442+664=\left(558+442\right)+\left(336+664\right)\)
\(=1000+1000=2000\)
5 x 25 x 2 x 37 x 4
= ( 5 x 2 ) x ( 25 x 4 ) x 37
= 10 x 100 x 37
= 1000 x 37
= 37000
\(\frac{120x999+120}{2x4x0,8x5x2,5x125}=\frac{120000}{10000}=12\)
\(27\cdot25\cdot\left(3+1\right)-230=27\cdot25\cdot4-230\)
1)
25 x 7 + 3 x (50-25) x (60 - 60)
=175 +3 x 25 x 0
=175
2)
\(\frac{1}{2}.\frac{3}{4}.\frac{4}{5}.\frac{1}{3}\\ =\frac{1.3.4.1}{2.4.5.3}\\ =\frac{3.4}{3.4.2.5}\\ =\frac{1}{2.5}\\ =\frac{1}{10}\)