A community for students.

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

anonymous

  • one year ago

4. If x = 20 when y = -4, find y when x = 10.

  • This Question is Closed
  1. ahsome
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Is this a linear equation, @dianolove?

  2. ahsome
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Wait, couldn't you do: \[\begin{align} y&=kx\\ -4&=k\times20\\ k&=\dfrac{-1}{5} \end{align}\]

  3. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    this is the question it asked me Suppose that x and y vary inversely. Write a function that models each inverse variation. Then use the equation to solve the problem.

  4. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Let's solve your equation step-by-step. 20x−4x=10 Step 1: Simplify both sides of the equation. 20x−4x=10 Simplify: (Show steps) 16x=10 Step 2: Divide both sides by 16. 16x16=1016 x=58 Answer: x=58

  5. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    do you under stand

  6. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    20x−4y=10

  7. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    *** x and y vary inversely*** means you can write the formula \[ y = \frac{k}{x} \]

  8. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    it is a inverse variation and your solving for y not x

  9. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    that formula is useful if we know what "k" is. to find k, we use the info If x = 20 when y = -4, find y when x = 10.

  10. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    in other words, replace x with 20 and y with -4 into the formula \[ -4= \frac{k}{20} \] and "solve for k" by multiplying both sides by 20

  11. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    can you find what k is ?

  12. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    k is -80

  13. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    yes, so now you know the formula (for this problem) is \[ y = \frac{-80}{x} \] find y when x = 10. to find y, replace x with 10 in the formula and simplify

  14. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    y=-8

  15. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    yes

  16. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    thanks phi will you keep helping me with these i got another one

  17. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    ok

  18. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    If x = 5 when , find y when x = 10.

  19. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    missing some info

  20. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    5. If x = 5 when y=-1 third , find y when x = 10.

  21. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    do you mean if x=5 when y = \( - \frac{1}{3} \) ?

  22. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    sorry mines will not do that but yes

  23. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    is k -30

  24. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    you could type it as y= -1/3 \[ y = \frac{k}{x} \\ - \frac{1}{3} = \frac{k}{5} \] to find k, multiply both sides by 5 \[ - \frac{1}{3} \cdot 5 = \frac{k}{5}\cdot 5 \\ - \frac{1}{3} \cdot 5 = k \cdot \frac{5}{5} \\ - \frac{5}{3} = k \]

  25. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    -15

  26. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    what is -15 ? k is -5/3

  27. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    oh i thought you said t multiply -5 into 3 , but what do you do now divide -5/3 into 10

  28. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    you write the formula \[ y = \frac{k}{x} \] and it might be easier to understand if you write it this way \[ y = k \cdot \frac{1}{x} \] which means the same thing. now replace k with -5/3 \[ y = - \frac{5}{3} \cdot \frac{1}{x} \]

  29. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    find y when x = 10. that means put in 10 for x in the formula \[ y = - \frac{5}{3} \cdot \frac{1}{x} \\ y = - \frac{5}{3} \cdot \frac{1}{10}\] and simplify

  30. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    y=6

  31. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    if you use a calculator on \[ - \frac{5}{3} \cdot \frac{1}{10} \] what do you get ?

  32. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    -1/6

  33. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    yes, y= -1/6 when x=10. It would be good to be able to do that without the calculator. when you multiply fractions, you multiply top times top and bottom times bottom \[ - \frac{5}{3} \cdot \frac{1}{10} = - \frac{5 \cdot 1 }{3 \cdot 10} \] we could multiply the bottom 3*10 to get 30 \[ - \frac{5}{30} \] and then simplify to get -1/6 or, it's easier to notice that 10 is 2*5 \[ - \frac{5 \cdot 1 }{3 \cdot 10} = - \frac{5 \cdot 1 }{3 \cdot 2 \cdot 5} \] and notice we have a 5 up top and down below, and they simplify to 5/5 = 1 \[ - \frac{1 }{3 \cdot 2} = - \frac{1}{6} \]

  34. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    what if x=-4/15 when y=-105,find x when y=4

  35. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[ y = k \cdot \frac{1}{x} \\ -105= k \cdot \frac{1}{-\frac{4}{15}} \]

  36. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    multiply both sides by -4/15,

  37. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    k=28

  38. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    so \[y = \frac{28}{x} \] find x when y=4 replace y with y \[ 4 = \frac{28}{x} \]

  39. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    first multiply both sides by x then divide both sides by 4

  40. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    7

  41. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    yes. \[ 4 x= \frac{28}{x} \cdot x \\ 4x = 28 \\\frac{4x}{4}= \frac{28}{4} \\x=7\]

  42. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    thanks are you getting tired of me asking questions

  43. phi
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 1

    no, but I do have to go. make a new post and someone will help you.

  44. anonymous
    • one year ago
    Best Response
    You've already chosen the best response.
    Medals 0

    ok thanks

  45. Not the answer you are looking for?
    Search for more explanations.

    • Attachments:

Ask your own question

Sign Up
Find more explanations on OpenStudy
Privacy Policy

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.