`@` `\text {Ans}`
`\downarrow`
`5,`
`a)`
`(290-x)*4=400`
`=> 290-x=400 \div 4`
`=> 290-x=100`
`=> x=290 - 100`
`=> x=190`
Vậy, `x=190`
`b)`
`x*3-2018 \div 2=23`
`=> 3x-1009=23`
`=> 3x=23+1009`
`=> 3x=1032`
`=> x=1032 \div 3`
`=> x=344`
Vậy, `x=344`
`c)`
`38*x-x*12-x*16=40`
`=> 38x-12x-16x=40`
`=> x(38-12-16)=40`
`=> x*10=40`
`=> x=40 \div 10`
`=> x=4`
Vậy, `x=4`
`d)`
`280-x*9-x=80`
`280-9x-x=80`
`=> 280-10x=80`
`=> 10x=280 - 80`
`=> 10x=200`
`=> x=200 \div 10`
`=> x=20`
Vậy, `x=20`
`e)`
`504 \div (16-3x) = 72`
`=> 16-3x=504 \div 72`
`=> 16-3x=7`
`=> 3x=16-7`
`=> 3x=9`
`=> x=9 \div 3`
`=> x=3`
Vậy, `x=3`
`f)`
`250 \div (2x-4)=145-120`
`=> 250 \div (2x-4) = 25`
`=> 2x-4=250 \div 25`
`=> 2x-4=10`
`=> 2x=10+4`
`=> 2x=14`
`=> x=14 \div 2`
`=> x=7`
Vậy, `x=7.`