Question

помогите пожалуйста математика​

Answer 1

6. (3 + 1/3) · (1 + 1/2) = 10/3 · 3/2 = 10/2 = 5 км

7. 34 + 45 – 12 – 25 = 79 – 37 = 42

8. 4,2x + 5 = –7,6 ⇔ 4,2x = –12,6 ⇔ x = –3

1.

$4 - \left(4\dfrac{21}{40} - 5.25\right):1\dfrac{9}{20} = 4 - \left(\dfrac{181}{40} - \dfrac{210}{40}\right):\dfrac{29}{20} = 4 + \dfrac{29}{40}\cdot\dfrac{20}{29} = 4 + \dfrac{1}{2} = 4\dfrac{1}{2}$

2.

$\dfrac{x+9}{3} = \dfrac{x-1}{5}\\\\(x+9)\cdot5 = (x-1)\cdot3\\\\5x + 45 = 3x - 3\\\\2x = -48\\\\x = -24$