Đáp án_Giải thích các bước giải:
Bài 1:
`a) 250*36=25*10*36=(25*36)*10=900*10=9000`
`b) 500*12=100*5*12=100*(5*12)=100*60=6000`
`c) 1200:50=(1000+200):50=1000:50+200:50=20+4=24`
`d) 900:25=9*100:25=9*4=36`
Bài 2:
`a) 34*15+34*85`
`=34*(15+85)`
`=34*100`
`=3400`
`b) 12*57+57*25+63*57`
`=57*(12+25+63)`
`=57*100`
`=5700`
`c) 36*28+36*82+64*69+64*41`
`=36*(28+82)+64*(69*41)`
`=36*110+64*110`
`=110*(36+64)`
`=110*100`
`=11000`
`d) 2*31*12+4*6*42+8*27*3`
`=(2*12)*31+(4*6)*42+(8*3)*27` (bước này bỏ cũng được nha)
`=24*31+24*42+24*27`
`=24*(31+42+27)`
`=24*100`
`=2400`
Bài 3:
`a) 250:(10-x)=25`
` 10-x=250:25`
` 10-x=10`
` x=10-10`
` x=0`
`b) 3*x-2018:2=23`
` 3*x-1009 =23`
` 3*x =23+1009`
` x =1032:3`
` x =344`
`c) (9x-21):3=2`
` 9x-21 =2*3`
` 9x-21 =6`
` 9x =6+21`
` 9x =27`
` x =27:9`
` x =3`
`d) 53*(9-x)=53`
` 9-x =53:53`
` 9-x =1`
` x =9-1`
` x =8`
