Câu 1 :
1/
a) 17,58 x 43 + 57 x 17,58
= 17,58 x (43 + 57)
= 17,58 x 100
= 1758.
b) 43,57 x 2,6 x (630 - 315 x 2)
= 43,57 x 2,6 x (630 - 630)
= 43,57 x 2,6 x 0
= 0.
c) $\frac{45 × 16 - 17}{45 × 15 + 28}$
= $\frac{45 × (1 + 15) - 17}{45 × 15 + 28}$
= $\frac{45 × 15 + 45 - 17}{45 × 15 + 28}$
= $\frac{45 × 15 + 28}{45 × 15 + 28}$
= 1.
d) 104 x 68 - 36 x 52
= 2 x 52 x 68 - 36 x 52
= 52 x (2 x 68) - 36 x 52
= 52 x 136 - 36 x 52
= 52 x (136 - 36)
= 52 x 100
= 5200.
2/
a) `23/27 và 22/29`
`23/27 > 23/29`
`Mà 23/29 > 22/29`
`=> 23/27 > 22/29`
b) `12/25 và 25/49`
`12/25 = 1 - 13/25`
`25/49 = 1 - 14/25`
`Vì 13/25 < 14/25`
`=> 1 - 13/25 > 1 - 14/25`
`=> 12/25 > 25/49`
Câu 2 :
a) (x × 0,25 + 1999) x 2000 = (53 + 1999) x 2000
x × 0,25 + 1999 = (53 + 1999) x 2000 : 2000
x × 0,25 + 1999 = 53 + 1999
x × 0,25 = 53 + 1999 - 1999
x × 0,25 = 53
x = 53 : 0,25
x = 212.
b) `71 + 65 × 4 = x + 140/x + 260`
`x + 140/x + 260 = 71 + 65 × 4`
`x + 140/x + 260 = 71 + 260`
`x + 140/x = 71`
`1 + 140/x = 71`
`140/x = 71 - 1`
`140/x = 70`
`x = 140 : 70`
`x = 2.`