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a,245 x 5 x 4=245x(5x4)=245x20=4900
b,2x125x4x5=(2x5)x(125x4)=10x500=5000
c,357x36+357x64=357x(36+64)=357x100=35700
d,542x68-28x542=542x(68-28)=542x40=21680
Hok tốt
a) 245 x 5 x 4
= ( 245 x 4 ) x 5
= 980 x 5
= 4900
b) 2 x 125 x 4 x 5
= ( 125 x 4 ) x ( 2 x 5 )
= 500 x 10
= 5000
c) 357 x 36 + 357 x 64
= 357 x ( 36 + 64 )
= 357 x 100
= 35700
d) 542 x 68 - 28 x 542
= 542 x ( 68 - 28 )
= 542 x 40
= 21680
a,15*(4+5)
c1
15*(4+5)
=15x9
=135
c2
15*(4+5)
=15x4+15x5
=60+75
=135
#hoktot
#hungb
a) 15 x (4 + 5)
= 15 x 9
= 135
15 x (4 + 5)
= 15 x 4 + 15 x 5
= 60 + 75
= 135
b) 45 x (8 - 5)
= 45 x 3
= 135
45 x (8 - 5)
= 45 x 8 - 45 x 5
= 360 - 225
= 135
a) 5 . 125 . 2 . 41 . 8
= (5 . 8) . (125 . 2) . 41
= 40 . 250 . 41
= 10 000 . 41
= 410 000
b) 25 . 7 . 10 . 4
= (25 . 4 ) . (10 . 7)
= 100 . 70
= 7000
Chúc bạn học tốt!! ^^
a,5.125.2.41.8=(125.8).(2.5).41=1000.10.41=410000
b,25.7.10.4=(25.4).70=100.70=7000
c,8.12.125.2=(8.125).12.2=100.24=2400
d,4.36.25.50=(4.25).(2.50).18=100.100.18=180000
\(a.\frac{19}{5}\cdot\frac{4}{7}+\frac{3}{7}\cdot\frac{19}{5}-\frac{4}{5}\)
\(=\frac{19}{5}\cdot\left(\frac{4}{7}+\frac{3}{7}\right)-\frac{4}{5}\)
\(=\frac{19}{5}\cdot1-\frac{4}{5}\)
\(=\frac{19}{5}-\frac{4}{5}=\frac{15}{5}=3\)
\(b.2\frac{2}{7}\cdot5\frac{2}{5}+\frac{16}{7}\cdot1\frac{3}{5}+\frac{1}{2}\)
\(=\frac{16}{7}\cdot\frac{27}{5}+\frac{16}{7}\cdot\frac{8}{5}+\frac{1}{2}\)
\(=\frac{16}{7}\cdot\left(\frac{27}{5}+\frac{8}{5}\right)+\frac{1}{2}\)
\(=\frac{16}{7}\cdot7+\frac{1}{2}\)
\(=16+\frac{1}{2}=\frac{33}{2}\)
\(c.\frac{3}{7}\cdot3\frac{3}{4}-\frac{3}{7}\cdot\frac{5}{4}-\frac{1}{4}\)
\(=\frac{3}{7}\cdot\frac{15}{4}-\frac{3}{7}\cdot\frac{5}{4}-\frac{1}{4}\)
\(=\frac{3}{7}\cdot\left(\frac{15}{4}-\frac{5}{4}\right)-\frac{1}{4}\)
\(=\frac{3}{7}\cdot\frac{5}{2}-\frac{1}{4}\)
\(=\frac{15}{14}-\frac{1}{4}=\frac{23}{28}\)
Chú ý: \(\cdot:\times\)
a) 105*x-20-18-16-...-2=19+17+15+...+3+1
105*x=1+2+3+4+...+20
105*x=\(\frac{\left(20+1\right)x20}{2}\)
105*x=210
x=2
Vậy x = 2
b) 1-6+11-16+21-26+...+91-96+101
=101-96+91-86+...+21-16+11-6+1
=(101-96)+(91-86)+...+(21-16)+(11-6)+1
=5+5+...+5+5+1 ( có (101-6):5+1);2=10 số 5)
=5x10+1=51
a)105xX-20-18-16-...-2=19+17+15+...+3+1
105xX-(20+18+16+...+2)=19+17+15+...+3+1
105xX-110=100
105xX=100+110
105xX=210
X=210:105
X=2
=1/5+2/5+51/85+4/5
=7/5+51/85
=119/85+51/85
=170/85=2
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a ) 2 x 3 x 4 x 8 x 50 x 25 x 125
= 3 x 2 x 50 x 4 x 25 x 8 x 125
= 3 x ( 2 x 50 ) x ( 4 x 25 ) x ( 8 x 125 )
= 3 x 100 x 100 x 1000
= 30000000
b ) 45 x 128 - 90 x 64
= 45 x ( 2 x 64 ) - 90 x 64
= ( 45 x 2 ) x 64 - 90 x 64
= 90 x 64 - 90 x 64
= 0
a) = (2.50).(4.25).(8.125).3=100.100.1000.3=30000000
b)45.128-90.64=45.128-45.2.64
=45.128-45.128
=0
a. Số số hạng: (64-1):3+1=22
Tổng:(64+1)x22=715
b. Số số hạng: (125-5):5+1=25
Tổng: (125+5)x25:2=1625
a) 1 + 4 + 7 +...+ 64
= \(\frac{\left[\left(64-1\right):3+1\right].\left(64+1\right)}{2}=\frac{1430}{2}=715\)
b) 5 + 10 + 15 +...+ 125
=\(\frac{\left[\left(125-5\right):5+1\right].\left(125+5\right)}{2}=\frac{3250}{2}=1625\)