Tell whether each equation represents a direct proportion. if so, identify the
constant of proportionality.

1. 0.4y = x

2. x = 1 - 2y

Step-by-step explanation:

1. 0.4y = x is a direct proportion.  It'd be more appropriate to write this as

   y =  x / 0.4, or y = 2.5x, in which case 2.5 is the constant of proportionality.

2. x = 1 - 2y is not a direct proportion because of the offset (1).  A line representing a direct proportion must go through the origin (0, 0); this particular line does not do that.

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional