a,(-30).7-14.(8-15)

=(-30).7-14.(-7)

=(-30).7-(-14).7

=7.[(-30)-(-14)]

=7.(-16)

=-112

b,(-13)+(-25)-6

=(-38)-6

=-44

c,125:(-25)+[(3-2^2)^2013].(-5)

=(-5)+[(3-4)^2013].(-5)

=(-5)+[(-1)^2013].(-5)

=(-5)+(-1).(-5)

=(-5).(-1+1)

=(-5).0

=0

d tính như bình thường nhé ( dùng máy tính cho nhanh)

\(\frac{\left(2^3.5.7\right).\left(5^2.7^3\right)}{\left(2.5.7^2\right)^2}\)
\(=\frac{\left(8.5.7\right).\left(25.7^3\right)}{4.25.7^4}\)
\(=\frac{280.25.7^3}{4.25.7^4}\)
\(=\frac{280}{4.7}\)
\(=\frac{280}{28}=10\)
 

(-5).8.(-2).(-125)

=[(-5).(-2)].[8.(-125)]

=10.(-1000)

=-10000

   48.(23-51)+51.(48-23)

= 48.23-48.51+51.48-51.23

= 48.23-51.23

= 23.(48-51)

= 23.(-3)

= (-69)

   1239-239.(-5)-5.239

= 1239.((-5)-5).239

= 1239.-10.239

= -2961210

a) \(227+50+23=\left(227+23\right)+50=250+50=300\)

b) \(135+360+65+40=\left(135+65\right)+\left(360+40\right)=200+400=600\)

c) \(1+2+3+4+5+...+97+98+99+100\)

\(=\left(100+1\right)+\left(99+2\right)+...+\left(50+51\right)\)

\(=101+101+101+...+101\)

\(=101\cdot50\)

\(\Leftrightarrow5050\)

d) \(115\cdot13-13\cdot15=13\cdot\left(115-15\right)=13\cdot100=1300\)

e) \(50-49+48-47+...+4-3+2-1\)

\(=\left(50-49\right)+\left(48-47\right)+...+\left(2-1\right)\)

\(=1+1+1+1+..+1\)

\(=1\cdot25\)

\(=25\)

f) \(30\cdot40\cdot50\cdot60=10\cdot3+10\cdot4+10\cdot5+10\cdot6\)

\(=10\cdot10\cdot10\cdot10\cdot3\cdot4\cdot5\cdot6\)

\(=10000\cdot360\)

\(=3600000\)

g) \(27\cdot36+27\cdot64=27\cdot\left(36+64\right)=27\cdot100=2700\)

h) \(5\cdot2^2-18:3=5\cdot4-18:3=20-6=14\)

i) \(13\cdot17-256:16+14:7-2021^0\)

\(=13\cdot17-4^4:4^2+2-1\)

\(=13\cdot17-16+2-1\)

\(=13\cdot17-17\)

\(=17\cdot\left(13-1\right)\)

\(=204\)

j) \(7^2-36:3=49-12=37\)