Bài $1$ :
$b)$
`7/8 : ( 2/9 - 1/18) + 7/8 : (1/36 - 5/12)`
`= 7/8 . 1/{2/9 - 1/18} + 7/8 . 1/{1/36 - 5/12}`
`= 7/8( 1/{2/9 - 1/18} + 1/{1/36 - 5/12})`
`= 7/8 ( 1/{ 1/6 } + 1/{-7/18} )`
`= 7/8 ( 6 + {-18}/7)`
`= 7/8 ( 42/7 + {-18}/7)`
`= 7/8 . 24/7`
`= 24/8`
`=3`
Bài `2` :
`b)`
`1+5+9+13+17 + ... +x = 5050`
`⇒[ (x - 1) :4 + 1 ] × [ (x+1) ] : 2 = 5050`
`⇒ [(x-1) : 4 +1] × (x+1) = 10100`
`⇒ {x-1+4}/{4} × (x+1) = 10100`
`⇒ {(x+3)(x+1)}/4 = 10100`
`⇒ (x+3)(x+1) = 40400 = 200 . 202`
`⇒ x = 199`
