`1.`
`1/5.8 + 1/8.11 + 1/11.14 + ... + 1/(x(x+3)) = 101/1540`
`=> 3/5.8 + 3/8.11 + 3/11.14 + ... + 3/(x(x+3))=303/1540`
`=> 1/5 - 1/8 + 1/8 - 1/11 + 1/11 - 1/14 + ... + 1/x - 1/(x+3) = 303/1540`
`=>1/5 -1/(x+3)=303/1540`
`=> 1/(x+3)=1/5 - 303/1540`
`=> 1/(x+3)= 1/308`
`=> x+3=308`
`=> x=305`
Vậy `x=305`
$\\$
`2.`
`x-((50x)/100 + (25x)/200 )=11 1/4`
`=> x-( (100x)/200 + (25x)/200) = 11 1/4`
`=> x- (125x)/200 = 45/4`
`=> (200x)/200 - (125x)/200 = 45/4`
`=> (75x)/200=45/4`
`=>75x . 4 = 200.45`
`=> 300x = 9000`
`=> x=30`
Vậy `x=30`
