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anonymous

  • 5 years ago

i need to know the answer to this suppose x varies directly as r, and x varies inversely as t. find t when r equals 10 and x equals -5, if t equals 20 when x equals 4 and r equals 2

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  1. amistre64
    • 5 years ago
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    So we are given this: x = r/t

  2. amistre64
    • 5 years ago
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    or really: x = kr/t where k is any constant, but lets make that constant a "1" for simplicities sake :)

  3. amistre64
    • 5 years ago
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    t = r/x then: t = 10/-5

  4. amistre64
    • 5 years ago
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    r = x/t r = 4/20

  5. anonymous
    • 5 years ago
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    its not rate over time. i need to find t!

  6. amistre64
    • 5 years ago
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    ack!! r = xt lol i forgot how to multiply :)

  7. amistre64
    • 5 years ago
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    r = 4(20)

  8. amistre64
    • 5 years ago
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    i see i forgot how to read the question as well..... let me start over :)

  9. amistre64
    • 5 years ago
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    Find t when r=10 and x= -5, if t=20 when x= 4 and r=2 whats this mean?

  10. anonymous
    • 5 years ago
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    its a variation function

  11. amistre64
    • 5 years ago
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    are you looking for the Constant? or what?

  12. amistre64
    • 5 years ago
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    4 = k(2/20) 40 = k x = 40r/t

  13. anonymous
    • 5 years ago
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    just finding the answer for t

  14. anonymous
    • 5 years ago
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    ?

  15. anonymous
    • 5 years ago
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    alright, hold on a minute and I will help, I just need to refresh my memory.

  16. anonymous
    • 5 years ago
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    First you need to set up a proportion. Since x varies directly as r and inversely as t, it will look like this:\[x_{1}t _{1} / r _{1} = x _{2}r _{2} / r _{2}\]

  17. anonymous
    • 5 years ago
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    You plug in your values, which would make \[(4)(20) / 2 = 5(t)/10\]

  18. anonymous
    • 5 years ago
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    or, 80 / 2 = 5t/10.

  19. anonymous
    • 5 years ago
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    you then solve the proportion by cross multiplying, like so: \[(80)(10) = 2(5t)\]

  20. anonymous
    • 5 years ago
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    or, 800 = 10t ; solving the equation leaves you with t = 80.

  21. anonymous
    • 5 years ago
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    hope that helps! ^-^

  22. amistre64
    • 5 years ago
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    -5 i think it was :) which makes it -80 right?

  23. anonymous
    • 5 years ago
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    ah true, thanks for pointing that out, I always get my signs messed up

  24. amistre64
    • 5 years ago
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    t = 400/-5 = -80

  25. amistre64
    • 5 years ago
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    i was just wondering if i did it right.... :)

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