Question

Calcule mentalmente o valor de x.

a) 3/15 = x/5

b) 8/x = 12/3

c) x+1/5 = 8/10

d) x-2/7 = 3/7

Answer 1

$(a)\frac{3}{15}=\frac{x}{5}\\\\15x=3\cdot5\\15x=15\\x=\frac{15}{15}\\x=1\\\\\\(b)\frac{8}{x}=\frac{12}{3}\\\\12x=3\cdot8\\12x=24\\x=\frac{24}{12}\\x=2\\\\\\(c)\frac{x+1}{5}=\frac{8}{10}\\\\10(x+1)=5\cdot8\\10x+10=40\\10x=40-10\\10x=30\\x=\frac{30}{10}\\x=3\\\\\\(d)\frac{x-2}{7}=\frac{3}{7}\\\\x-2=3\\x=3+2\\x=5$



Espero ter ajudado.
Bons estudos! :)

Answer 2

Resposta:

A) x = 1               B) x = 2               C) x = 3                D) x = 5

Explicação passo-a-passo:

A)  $\left \ {{3 --- x} \atop {15 --- 5}} \right.$

15x = 3 · 5

15x = 15

x = $\frac{15}{15}$

x = 1

B) $\left \ {{8 --- 12} \atop {x --- 3}} \right.$

12x = 3 · 8

12x = 24

x = $\frac{24}{12}$

x = 2

C)   $\left \ {{x + 1 --- 8} \atop {5 --- 10}} \right.$

10(x + 1) = 5 · 8

10x + 10 = 40

10x = 40 - 10

10x = 30

x = $\frac{30}{10}$

x = 3

D)   $\left \ {{x - 2 --- 3}} \atop {7 --- 7}} \right.$

x - 2 = 3

x = 3 + 2

x = 5