Question

multiple choice question! please help!
Suppose y varies directly with x, and y = 14 when x = –4. What is the value of y when x = –6?

–21
10
18
21

Answer 1

y varies directly with x

means that

y = kx

Answer 2

when x = -4, y is y = 14

so

y = kx

turns into

14 = k*(-4)

Answer 3

solve for k and tell me what you get

Answer 4

-3.5, But I think Im wrong..

Answer 5

you're correct

Answer 6

so

y = kx

turns into

y = -3.5x

Answer 7

now they want to know the value of y when x = -6

Answer 8

so

y = -3.5x

y = -3.5(-6)

y = ???

Answer 9

21.

Answer 10

thank yoouuu!:))

Answer 11

nailed it

Answer 12

can you walk me through this one too?
Suppose y varies directly with x, and y = 25 when x = 140. What is the value of x when y = 36?

Answer 13

y varies directly with x

means what

Answer 14

y=kx

Answer 15

good

Answer 16

we're given x = 140 and y = 25

so

y = kx

becomes

25 = k*140

Answer 17

so k = ____

Answer 18

.18

Answer 19

I would use more decimal places for k. I'm going to use k = 0.17857

so

y = kx

becomes

y = 0.17857x

Now plug in y = 36 and solve for x

y = 0.17857x

36 = 0.17857x

36/ 0.17857 = x

201.601613 = x

x = 201.601613

now round to the nearest tenth to get 201.6

this is the same as 201 and 3/5 or the improper fraction 1008/5

Answer 20

optionally...

y = kx

25 = k*140

25/140 = k

k = 25/140

k = 5/28

--------------------

y = kx

y = (5/28)x

36 = (5/28)*x

36*28 = 5x

1008 = 5x

5x = 1008

x = 1008/5


So x = 1008/5 which is x = 201.6 in decimal form