Repede please.Am nevoie acum!

[tex] \frac{8a-7b}{6a+5b}=\frac{4}{5} \\ \\ 5(8a-7b)=4(6a+5b)\\ \\ 40a-35b=24a+20b\\ \\ 40a-24a=20b+35b\\ \\16a=55b\\ \\ \frac{a}{b}= \frac{55}{16} [/tex]

2. {x;y} i.p {2;4}

[tex] \frac{x}{2}=\frac{y}{4}=k [/tex]

x=2×k si y =4×k

Media aritmetica = 30 deci Ma=(x+y):2=30⇒putem afla suma numerelor :x+y=2×30=60

2k+4k=60

6k=60

k=10

dar x=2k=2×10=20 si y=4k=4×10=40

deci x=20 si y=40

3. pretul final este 80

100%-20% reducere)=80%

daca 80% reprezinta 80 lei

atunci 100% reprezinta x lei

deci x=(100×80):80100 lei inainte de ultima reducere

80%................100 lei

atunci 100%.........y lei

y= (100 ×100);80=125 lei a valorat inainte de cele 2 reduceri

Аноним Аноним · Answer 2 · 2018-08-13T10:20:40+03:00

[tex] \it 1)\ \ \dfrac{8a-7b}{6a+5b} = \dfrac{4}{5} \Rightarrow 40a-35b=24a+20b \Rightarrow 16a=55b \Rightarrow \dfrac{a}{b}=\dfrac{55}{16}\\ \\ \\ 2)\ \ m_a=\dfrac{x+y}{2} = 30 \Rightarrow x+y=60\ \ \ \ \ (1)\\ \\ \\ \{x,\ y\}\ i.\ p.\ \{2,\ 4\} \Rightarrow 2x=4y|_{:2} \Rightarrow x=2y \ \ \ \ \ (2)\\ \\ \\ (1), \ (2) \Rightarrow 2y+y=60 \Rightarrow 3y = 60 \Rightarrow y=20\ \ \ \ (3)\\ \\ \\ (2), \ (3) \Rightarrow x=2\cdot20 \Rightarrow x = 40\\ \\ \\ Numerele \ \ sunt: x = 40, \ y=20 [/tex]

[tex] \it 3)\ Not\breve{a}m\ x- pre\c{\it t}ul\ ini\c{\it t}ial.\ \ 20\% =\dfrac{20}{100} =\dfrac{1}{5}\\ \\ \\ I)\ Dup\breve{a}\ prima\ reducere, \ pre\c{\it t}ul\ \ devine:\\ \\ \\ x-\dfrac{x}{5} =\dfrac{4x}{5}\\ \\ \\ II)\ Dup\breve{a}\ a\ doua\ reducere, \ pre\c{\it t}ul\ \ devine:\\ \\ \\ \dfrac{4x}{5} -\dfrac{1}{5}\cdot\dfrac{4x}{5} = \dfrac{4x}{5} - \dfrac{4x}{25} = \dfrac{20x-4x}{25} =\dfrac{16x}{25}. [/tex]

Dar, ultimul preț este 80 lei, deci:

[tex] \it \dfrac{16x}{25} =80 \Rightarrow \dfrac{16}{25}x =80 \Rightarrow x = 80\cdot\dfrac{25}{16} \Rightarrow x = 125\ lei [/tex]