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a) 72 + 9 + 8 = ( 72 + 8 ) + 9
= 80 + 9
= 89
b)37 + 18 + 3 = ( 37 + 3 ) + 18
= 40 + 18
= 58
c) 48 + 26 + 4 = 48 + (26 + 4)
= 48 + 30
= 78
d)85 + 99 + 1 = 85 + ( 99 + 1 )
= 85 + 100 = 185
e) 67 + 98 + 33 = ( 67 + 33 ) + 98
= 100 + 98 = 198
= ( 11 + 89 ) + ( 22 + 78 ) + ( 33 + 67 ) + ( 44 + 56 ) + 55
= 100 + 100 + 100 + 100 + 55
= 400 + 55
= 455
HT
phuonglebao9@gmail.com
=<89+11>+<78+22>+<67+33>+<56+44>+55
=100+100+100+100+55
=400+55
=455
a) \(19\times\left(52+38\right)-9\times\left(52+38\right)=\)
\(=\) \(19\times90-9\times90\)
\(=90\times\left(19-9\right)\)
\(=90\times10\)
\(=900\)
b) \(\dfrac{2}{5}\div\dfrac{3}{7}\times\dfrac{3}{7}\div\dfrac{2}{5}+2019=\)
\(=\left(\dfrac{2}{5}\div\dfrac{2}{5}\right)\times\left(\dfrac{3}{7}\div\dfrac{3}{7}\right)+2019\)
\(=1\times1+2019\)
\(=2019\)
a: \(=\dfrac{21}{11}+\dfrac{12}{11}+\left(-\dfrac{9}{19}-\dfrac{3}{19}-\dfrac{6}{19}\right)=3-\dfrac{18}{19}=\dfrac{39}{19}\)
b: \(=\dfrac{2}{3}+\dfrac{4}{3}+\dfrac{3}{4}+\dfrac{7}{4}+\dfrac{4}{5}+\dfrac{16}{5}=2+4+\dfrac{5}{2}=6+\dfrac{5}{2}=\dfrac{17}{2}\)
\(1235\text{×}6789\text{×}\left(630-315\text{×}2\right)\)
\(=1235\text{×}6789\text{×}\left(630-630\right)\)
\(=1235\text{×}6789\text{×}0=0\)
\(\left(100+67\right)\text{×}67+\left(200-38\right)\text{×}33\)
\(=167\text{×}67+167\text{×}33\)
\(=167\text{×}\left(67+33\right)\)
\(=167\text{×}100=16700\)
\(72+36\text{×}2+24\text{×}3+18\text{×}4+12\text{×}2+168\)
\(=72+72+72+72+24+168\)
\(=\left(72\text{×}4\right)+24+168=288+24+168=480\)
\(19\) x \(\left(52+38\right)-9\) x \(\left(52+38\right)\)
\(=19\) x \(90-9\) x \(90\)
\(=\left(19-9\right)\) x \(90\)
\(=10\) x \(90\)
\(=900\)
a) 96 + 78 + 4 = 96 + 4 + 78 = 100 + 78 = 178
67 + 21 + 79 = 67 + 100 = 167
408 + 85 + 92 = 405 + 92 + 85 = 500 + 85 = 585
b) 789 + 285 + 15 = 789 + 300 = 1089
448 + 594 + 52 = 448 + 52 + 594 = 500 + 594 = 1094
677 + 969 + 123 = 677 + 123 + 969 = 1769
a) 96 + 78 + 4 = 96 + 4 + 78 = 100 + 78 = 178
67 + 21 + 79 = 67 + 100 = 167
408 + 85 + 92 = 405 + 92 + 85 = 500 + 85 = 585
b) 789 + 285 + 15 = 789 + 300 = 1089
448 + 594 + 52 = 448 + 52 + 594 = 500 + 594 = 1094
677 + 969 + 123 = 677 + 123 + 969 = 1769
Hướng dẫn giải:
a) 93 + 39 + 7 = (93 + 7) + 39 = 100 + 39 = 139.
89 + 85 + 11 = (89 + 11) + 85 = 100 + 85 = 185
184 + 66 + 16 = (184 + 16) + 66 = 200 + 66 = 266
b) 23 + 52 + 47 + 98 = (23 + 47) + (52 + 98) = 70 + 150 = 220
16 + 490 + 84 + 10 = (16 + 84) + (490 + 10) = 100 + 500 = 600