Question

1. The value of y varies directly with x. If x=3, then y = 21. What is the value of x when y = 105? A. 3/5 B.3 C. 7 D. 15

Pls help I been working on this for forever now.

Answer 1

"The value of y varies directly with x" ----> y = kx
when x=3, y=21
21 = k(3)
k = 7

so we have y = 7x

plug in y= 105 and solve for x

Answer 2

Um......I guess my answer for this equation or problem would be D. 15. Pls let me know if I am wrong.

Answer 3

15 is the correct answer.
Why are you confused. What I did is the standard way of handling direct variations.

You could set up a ratio .....
y1/y2 = x1/x2
in your case x1=3 and y1 =21
find x2 when x2 = 105

21/105 = 3/x2
cross-multiply
21x2 = 315
x2 = 315/21 = 15

Answer 4

Reiny thanks so much. But I need help with one more thing.

Answer 5

9. What is the equation in slope-intercept form of the line that passes through the point (5,0) and is parallel to the line represented by y=1.2x+3.8? And just for a note The slopes of a parallel line are the same. A. y=1.3x-6 B. y=-1.2x+6 C. y=1.2x+5 D. y = 1.2x-5
My answer is um....B

Answer 6

y=1.2x+3.8 has slope 1.2
Now use the point-slope form for your desired line:
y-5 = 1/2 (x-0)

So, not B.

Answer 7

so what is the slope then?

Answer 8

the answer is D. 15

Answer 9

It would be D 15 because it is a proportion so it would be

3/21=x/105

Answer 10

For a line equation for the form of y = mx + b, the slope is m,

m in this equation (y = 1.2x + 3.8) is 1.2,

It is not equation A since it has a slope of 1.3,

It is not equation B since it has a slope of -1.2 which makes it cross over line y = 1.2x + 3.8. (perpendicular)

Answer 11

It would not be D even though it has a slope of 1.2. (for other answers with the same slope don't assume it is correct without proof!) The y values don't match up. (find some points on the line and compare them with the equation y = 1.2x + 3.8; look at the bottom for how to find points on a line.)

C is the answer. Take the equations y = 1.2x + 5 and y = 1.2x + 3.8 and make tables with them. As you can see the y values line up.

Equation C (y = 1.2x + 5) Equatioion y = 1.2x + 3.8

x y x y
-1 2.6 -2 2.6
0 3.8 -1 3.8
1 5 0 5
2 6.2 1 6.2
3 7.4 2 7.4



Finding Points on a Line
To find points on the line y = mx + b,

Choose x and solve the equation for y,

Example,
Find two points on the line y = 1.2x + 3.8:

Let x =1. Substitute x = 1 into y = 21.x + 3.8 and solve for y,

y = 1.2(1) + 3.8 = 1.2 + 3.8 = 5

(1,5)