Question

The variables y and x have a proportional relationship, and y = 7 when x = 2.

What is the value of y when x = 5?



The variables y and x have a proportional relationship, and y = 7 when x = 2.

What is the value of x when y = 21?




Which equation represents a proportional relationship?


y=−x

y=−5(x+1)

y = 5x + 1

y=15x

Answer 1

17.5

i just did it on my quiz and it was wrong(the other guy is wrong)

Answer 2

y= 35/2 when x=5

x=6 when y =21

Proportinal relatiionships: y=−x , y=15x

Explanation:

The formula for direct variation is

y= kx

If y=7 and x=2, we can solve for k

7 =k*2

Divide by 2

7/2 =k

y =7/2 x

Now if x=5

y =7/2 * 5

y =35/2

Now if y=21

21 =7/2 * x

Multiply by 2/7

21 * 2/7 = 7/2 * 2/7 x

6 =x

Which equation represents a proportional relationship?

y=−x

YES k = -1 Some people debate about having a negative constant, but everything I have read and taught says you can have a negative constant.

y=−5(x+1)

This does not go through the origin so no

if x=0 y = -5

y = 5x + 1

if x = 0 y =1 so no

y=15x

YES k = 15