Bài 1:
a: \(341\cdot67+341\cdot16+659\cdot83\)
\(=83\cdot341+659\cdot83=83\cdot1000=83000\)
b: \(42\cdot53+47\cdot156-47\cdot114\)
\(=42\cdot53+47\cdot42\)
\(=42\cdot100=4200\)
bài 2:
a: 135+260+65+40
=135+65+260+40
=200+300
=500
b: 463+318+127+22
=463+127+318+22
=590+340=930
c: 20+21+22+...+29+30
=(20+30)+(21+29)+(22+28)+(23+27)+(24+26)+25
=50+50+50+50+50+25
=275
Bài 3:
a: (x-12):5=2
=>\(x-12=5\times2=10\)
=>x=12+10=22
b: \(\left(20-x\right)\times5=15\)
=>20-x=15:5=3
=>x=20-3=17
c: \(\left(x-34\right)\times15=0\)
=>x-34=0
=>x=34
d: \(18\times\left(x-16\right)=18\)
=>x-16=1
=>x=1+16=17
Bài `1`
\(a,341.67+341.16+659.83\)
\(=341.\left(67+16\right)+659.83\)
\(=341.83+659.83\)
\(=\left(341+659\right).83\)
\(=1000.83\)
\(=8300\)
\(b,42.58+47.156-47.114\)
\(=42.58+47.\left(156-114\right)\)
\(=42.58+47.42\)
\(=42.\left(58+47\right)\)
\(=42.105\)
\(=4410\)
Bài `2`
\(a,135+260+65+40\)
\(=\left(135+65\right)+\left(260+40\right)\)
\(=200+300\)
\(=500\)
\(b,463+318+127+22\)
\(=\left(463+127\right)+\left(318+22\right)\)
\(=590+340\)
\(=930\)
\(c,20+21+22+23+...+29+30\)
\(=\left(20+30\right)+\left(21+29\right)+\left(22+28\right)+\left(23+27\right)+\left(24+26\right)+25\)
\(=50+50+50+50+50+25\)
\(=50\times5+25\)
`= 250 + 25`
`= 275`
Bài `3`
\(a,\left(x-12\right):5=2\)
\(x-12=2\times5\)
\(x-12=10\)
\(x=10+12\)
\(x=22\)
\(b,\left(20-x\right)\times5=15\)
\(20-x=15:5\)
\(20-x=3\)
\(x=20-3\)
\(x=17\)
\(c,\left(x-34\right)\times15=0\)
\(x-34=0:15\)
\(x-34=0\)
\(x=0+34\)
` x = 34`
`d, 18` \(\times\left(x-16\right)=18\)
`x - 16 = 18 : 18`
` x - 16 = 1`
` x = 1 + 16`
` x = 17`
