Question

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

Answer 1

So we are given this:

x = r/t

Answer 2

or really:

x = kr/t where k is any constant, but lets make that constant a "1" for simplicities sake :)

Answer 3

t = r/x then:

t = 10/-5

Answer 4

r = x/t

r = 4/20

Answer 5

its not rate over time. i need to find t!

Answer 6

ack!! r = xt lol i forgot how to multiply :)

Answer 7

r = 4(20)

Answer 8

i see i forgot how to read the question as well..... let me start over :)

Answer 9

Find t when r=10 and x= -5, if t=20 when x= 4 and r=2 whats this mean?

Answer 10

its a variation function

Answer 11

are you looking for the Constant? or what?

Answer 12

4 = k(2/20)

40 = k

x = 40r/t

Answer 13

just finding the answer for t

Answer 14

?

Answer 15

alright, hold on a minute and I will help, I just need to refresh my memory.

Answer 16

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

Answer 17

You plug in your values, which would make
\[(4)(20) / 2 = 5(t)/10\]

Answer 18

or, 80 / 2 = 5t/10.

Answer 19

you then solve the proportion by cross multiplying, like so:
\[(80)(10) = 2(5t)\]

Answer 20

or, 800 = 10t ; solving the equation leaves you with t = 80.

Answer 21

hope that helps! ^-^

Answer 22

-5 i think it was :) which makes it -80 right?

Answer 23

ah true, thanks for pointing that out, I always get my signs messed up

Answer 24

t = 400/-5 = -80

Answer 25

i was just wondering if i did it right.... :)