bài `4` :

`a)` `2.(5.4^2 - 18 ) 

`=2.(5.16 - 18)`

`=2(80-18)`

`=2 . 62 `

`=124`

`b)` `20-[30-(5-1)^2]`

`=20-[30-4^2]`

`=20-[30-16]`

`=20 - 14`

`=6`

`c)` `5[(85-35:7):8+90]-50`

`=5[(85-5):8+90]-50`

`=5[80:8+90]-50`

`=5[10+90]-50`

`=5 . 100 - 50`

`=500 - 50`

`=450`

`d)` `2.[(7-3^3:3^2) : 2^2 + 99]-100`

`=2.[(7-3) : 2^2 + 99]-100`

`=2.[5 : 2^2 + 99]-100`

`=2.[5 : 4 + 99]-100`

`=2.[1,25 + 99]-100`

`=2 . 100,25 -100`

`=200,5 -100`

`=100,5`

`e)` `(28.27^[2020] - 27^[2020] ) : 27^[2021]`

`=(28.27^[2020] - 27^[2020] . 1 ) : 27^[2021]`

`=[27^[2020] . (28-1)]  : 27^[2021]`

`=[27^[2020] . 27 ] : 27^[2021]`

`=27^[2021]  : 27^[2021]`

`=1`

bài `5` :

`a)` `142 - [50-(2^3 . 10 - 2^3 .5)]`

`=142 - [50-(8 . 10 -8 .5)]`

`=142 - {50-[8 . (10-5)]}`

`=142 - {50-[8 . 5]}`

`=142 - {50-40}`

`=142 - 10`

`=132`

`b)` `375 : {32-[4+(5 . 3^2 -42)]}-14`

`=375 : {32-[4+(5 . 9 -42)]}-14`

`=375 : {32-[4+(45 -42)]}-14`

`=375 : {32-[4+3]}-14`

`=375 : {32-7}-14`

`=375 : 25-14`

`=15-14`

`=1`

`c)` `{210 : [16+3(6+3.2^2)]}-3`

`={210 : [16+3(6+3.4)]}-3`

`={210 : [16+3(6+12)]}-3`

`={210 : [16+3.18]}-3`

`={210 : [16+54]}-3`

`={210 : 70 } - 3`

`=3 - 3 `

`=0`

`d)` `12 : { 400 : [500 - (125 + 25.7)]}`

`=12 : {400 : [ 500 - (125 + 175)]}`

`= 12 : {400:[500-300]}`

`=12 : { 400 : 200}`

`=12 : 2`

`=6`