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a: =100x26=2600
b: =78x10=780
c: =67x100=6700
d: =1000x575=575000
\(4\times26\times25=\left(4\times25\right)\times26=100\times26=2600\\ 63\times78-53\times78=\left(63-53\right)\times78=10\times78=780\\ 67\times92+67\times8=67\times\left(92+8\right)=67\times100=6700\\ 8\times23\times25\times125=\left(8\times125\right)\times\left(23\times25\right)=1000\times575=57500\)
\(1235\text{×}6789\text{×}\left(630-315\text{×}2\right)\)
\(=1235\text{×}6789\text{×}\left(630-630\right)\)
\(=1235\text{×}6789\text{×}0=0\)
\(\left(100+67\right)\text{×}67+\left(200-38\right)\text{×}33\)
\(=167\text{×}67+167\text{×}33\)
\(=167\text{×}\left(67+33\right)\)
\(=167\text{×}100=16700\)
\(72+36\text{×}2+24\text{×}3+18\text{×}4+12\text{×}2+168\)
\(=72+72+72+72+24+168\)
\(=\left(72\text{×}4\right)+24+168=288+24+168=480\)
`5 xx 74 xx 2 = 5xx 2 xx 74 = 10xx74 = 740`
`4xx196xx5 = 4xx5xx196 = 20xx196 = 3920`
`(50 + 25)xx4 = 50xx4 + 25xx4 = 200 + 100 = 300`
`125xx(80+8) = 125xx80 + 125xx8 = 10000 + 1000 = 11000`
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
a) 1 267 + 99 + 501 = 1 267 + (99 + 501)
= 1 267 + 600 = 1 867
25 x 14 x 4 = (25 x 4) x 14
= 100 x 14 = 1 400
b) 3 905 x (50 – 1) = 3 905 x 50 – 3 905 x 1
= 195 250 – 3 905 = 191 345
270 : ( 27 x 2 ) = 270 : 27 : 2
= 10 : 2 = 5
c) 115 x 58 + 115 x 42 = 115 x (58 + 42)
= 115 x 100 = 11 500
136 x 67 – 136 x 66 = 136 x (67 – 66)
= 136 x 1 = 136
a) 216 x 5 x 2
= 216 x (5x2)
= 216 x 10 = 2160
b) 4 x 76 x 25
= (4 x 25) x 76
= 100 x 76 = 7600
c) 5 x 19 x 2
= ( 5 x2 ) x 19
= 10 x 19 = 190
d) 125 x 23 x 8
= ( 125 x 8) x 23
= 1000 x 23 = 23000
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