Tính bằng cách hợp lý:
-58.(-42) + 42.12 =
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17 x 42 + 67 x 58 - 50 x 28
= 714 + 3886 - 1400
= 4600 - 1400
= 3200
17x42+67x58-50x28
= (42+58) x (67-17)-(50x28)
= 100 x 50 - 1400
= 5000 - 1400
= 3600
`@` `\text {Ans}`
`\downarrow`
`2023 \times 14 + 2023 \times 83+97`
`= 2023 \times (14+83) + 97`
`= 2023 \times 97 + 97`
`= 196231 +97`
`= 196328`
`78 \times 31+78 \times 24+78 \times 17+78 \times 22 \times 72`
`= 78 \times (31+24+17+22 \times 72)`
`= 78 \times (31+24+17+1584)`
`= 78 \times 1656`
`= 129168`
`371 \times 69+371 \times 14+629 \times 83`
`= 371 \times (69+14) + 629 \times 83`
`= 371 \times 83 + 629 \times 83`
`= 83 \times (371+629)`
`= 83 \times 1000`
`= 83000`
`91 \times 51+49 \times 163-49 \times 72`
`= 91 \times 51 + 49 \times (163-72)`
`= 91 \times 51+49 \times 91`
`= 91 \times (51+49)`
`= 91 \times 100`
`= 9100`
`3 \times 12 \times 17 + 4 \times 9 \times 81 + 2 \times 6 \times 6`
`= 9 \times 4 \times 17 + 4 \times 9 \times 81 + 4 \times 9 \times 2`
`= 9 \times 4 \times (17+81+2)`
`= 36 \times 100`
`= 3600`
`42 \times 17 + 58 \times 83 \times 42 \times 83 + 42 \times 83 + 17`
`= 17 \times (42+58) + 42 \times 83 \times (58 \times 83 +1)`
`= 17 \times 100 + 3486 \times 4815`
`= 1700 + 16785090`
`= 16786790`
42.(-93)+93.52
=42.(-93)+(-93).(-52)
=(-93).[42+(-52)
=(-93).(-10)
=930
42.(-93)+93.52
= 42 . (-93) + (-93) . (-52)
= (-93) . [42+(-52)]
= (-93) . (-10)
= 930
\(26\times\dfrac{13}{42}:13\\ =26\times\dfrac{13}{42}\times\dfrac{1}{13}\\ =26\times\dfrac{1}{42}=13\times\dfrac{1}{21}=\dfrac{13}{21}\)
1. Q=165+247+528+125+315
= 100+60+5+200+40+7+500+20+8+100+20+5+300+10+5
= ( 100+200+500+100+300) + ( 60+40+20+20+10 ) +( 5+7+8+5+5 )
= 1200+150+30
=1280
R=1234+5678+8+80
=1000+200+30+4+5000+600+70+8+8+80
= ( 1000+5000) + ( 200+600 ) + (30+70+80) + ( 4+8+8)
=6000+800+180+20
=7000
Bài 1
Tính : Q=165+247+528+125+315
=(165+125)+(247+315+528)
=290+1090
= 1380
R=1234+5678+8+80
=(1234+6)+(5678+2)+80
= 1240+5680+80
= (1240+60)+(5680+20)
=1300+5700=7000
Bài 2:
A= 243-97=(243+7)-(97-7)=250-90=160
B= 400-42-58=400-(42+58)=400-100=300
C=600-67-33=600-(67+33)=600-100=500
D=200-24-46=200-(24+46)=200-70=130
E=400-5-6-7-8=400-(5+6+7+8)=400-26=374
F= 764-115-268-43-32-20-85-37
=764-(115+85)-(268+32)-(43+37)-20
=764-200-300-80-20
=164
G=350-7-18-52-48-72
=350-(18+72)-(52+48)-7
=350-90-100-7
=160-7
=153
-58.(-42) + 42.12
= 58.42 + 42.12
= 42.(58+12)
= 42.70
= 2940