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a: =100x26=2600
b: =78x10=780
c: =67x100=6700
d: =1000x575=575000
\(4\times26\times25=\left(4\times25\right)\times26=100\times26=2600\\ 63\times78-53\times78=\left(63-53\right)\times78=10\times78=780\\ 67\times92+67\times8=67\times\left(92+8\right)=67\times100=6700\\ 8\times23\times25\times125=\left(8\times125\right)\times\left(23\times25\right)=1000\times575=57500\)
\(1235\text{×}6789\text{×}\left(630-315\text{×}2\right)\)
\(=1235\text{×}6789\text{×}\left(630-630\right)\)
\(=1235\text{×}6789\text{×}0=0\)
\(\left(100+67\right)\text{×}67+\left(200-38\right)\text{×}33\)
\(=167\text{×}67+167\text{×}33\)
\(=167\text{×}\left(67+33\right)\)
\(=167\text{×}100=16700\)
\(72+36\text{×}2+24\text{×}3+18\text{×}4+12\text{×}2+168\)
\(=72+72+72+72+24+168\)
\(=\left(72\text{×}4\right)+24+168=288+24+168=480\)
a, 2019 x (2 x 5)
= 2019 x 10
= 20 190
b, (5 x 2) x (8 x 125) x 9
= 10 x 1000 x 9
= 90 000
c, (4 x 25) x 2019
= 100 x 2019
= 201 900
d, (50 x 2) x (125 x 8) x 202
= 100 x 1000 x 202
= 20 200 000
a) 2019 x 2 x 5
= (2 x 5) x 2019
= 10 x 2019
= 20190b) 5 x 8 x 9 x 2 x 125
= (5 x 2) x (125 x 8) x 9
= 10 x 1000 x 9
= 10000 x 9
= 90000
c) 4 x 2019 x 25
= (4 x 25) x 2019
= 100 x 2019
= 201900
d) 50 x 125 x 2 x 8 x 202
= (50 x 2) x (125 x 8) x 202
= 100 x 1000 x 202
= 100000 x 202
= 20200000
\(\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{49.50}\)
\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{49}-\dfrac{1}{50}\)
\(=\dfrac{1}{2}-\dfrac{1}{50}=\dfrac{12}{25}\)
a) 4 x 78 x 5
= (4 x 5) x 78
= 20 x 78
= 1560
b) 2 x 99 x 5
= (2 x 5) x 99
= 10 x 99
= 990
25 x 67 x 4 = ( 25 x 4) x 67 = 100 x 67 = 6700
125 x 2 x 4 = ( 125 x 4) x 2 = 500 x 2 = 1000
67 x 5 x 2 = 67 x ( 5x2) = 67 x 10 = 670
50 x 78 x 2= ( 50 x 2) x 78 = 100 x78 = 7800
25 x 67 x 4 = (25 x 4) x 67 = 100 x 67 = 6700
125 x 2 x 4 = ( 125 x 4 ) x 2 = 500 x 2 = 1000
67 x 5 x 2 = 67 x ( 5 x 2) = 67 x 10 = 670
50 x 78 x 2 = ( 50 x 2 ) x 78 = 100 x 78 = 7800