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) 3/15 = x/5
1/5=x/5
1=x
x=1

b)8/x=12/3
8/x=4
8/x=4, x≠0

8=4x
4x=8
x=2, x≠0
x=2

Answer 2

Calcule mentalmente o valor de x.

FRAÇÃO  igual FRAÇÃO  ( só cruzar)


a) 3/15 = x/5

3     x
--- = ----
15    5

15(x) = 3(5)
15x = 15
x = 15/15
x = 1


b) 8/x = 12/3

8         12
----- = ------
  x        3

12(x) = 3(8)
12x = 24
x = 24/12
x = 2

c) x+1/5 = 8/10

x + 1       8
------ = ------
   5        10

10(x + 1)= 5(8)
10x + 10 = 40
10x = 40 - 10
10x  =  30
x = 30/10
x = 3



d) x-2/7 = 3/7

x - 2        3
------ = -------
  7           7

7(x - 2) = 7( 3)
7x - 14 = 21
7x = 21 - 14
7x = 7
x = 7/7
x = 1